Developmental Anatomy — MCQs

Developmental Anatomy Indian Medical PG Practice Questions and MCQs

Question 61: At what stage of fetal development do the testes descend through the inguinal canal?

A. 4 months
B. 5 months
C. 9 months
D. 7 months (Correct Answer)

Explanation: 7 months - Testicular descent typically begins around the **seventh month of gestation**, guided by the gubernaculum, through the **inguinal canal** into the scrotum. - This process is crucial for proper testicular function, as the cooler scrotal environment is necessary for **spermatogenesis** [1]. *4 months* - At this stage, the testes have not yet begun their full descent and are usually located in the **abdominal cavity**, near the kidneys. - While hormonal influences are beginning, the **gubernaculum** has not yet fully matured to guide the descent. *5 months* - The testes are still generally confined to the **abdominal cavity** at this point, though some early preparatory changes for descent may be occurring. - Significant **descent through the inguinal canal** has not yet commenced. *9 months* - By the ninth month, or term gestation, the testes should have **completed their descent** and are typically found within the **scrotum** [1]. - If descent has not occurred by this time, it is considered **cryptorchidism** [1].

Question 62: Styloid process is derived from?

A. Second pharyngeal arch (Correct Answer)
B. First pharyngeal arch
C. Third pharyngeal arch
D. Fourth pharyngeal arch

Explanation: **Second pharyngeal arch** - The **styloid process** of the temporal bone is derived from the **cartilage of the second pharyngeal arch**, also known as Reichert's cartilage. - This arch also contributes to the **lesser horn** and upper part of the body of the **hyoid bone**, the stapes, and several muscles of facial expression. *First pharyngeal arch* - The first pharyngeal arch, or **Meckel's cartilage**, gives rise to the **malleus** and **incus** of the middle ear. - It also forms the **mandible** and maxilla. *Third pharyngeal arch* - The third pharyngeal arch contributes to the **greater horn** and lower part of the body of the **hyoid bone**. - It does not form the styloid process. *Fourth pharyngeal arch* - The fourth pharyngeal arch contributes to the **laryngeal cartilages**, specifically parts of the **thyroid** and **cricoid cartilages**. - It is not involved in the formation of the styloid process.

Question 63: Stroma of cornea develops from ?

A. Neural ectoderm
B. Surface ectoderm
C. Mesoderm
D. Neural crest (Correct Answer)

Explanation: ***Neural crest*** - The **stroma of the cornea**, along with the corneal endothelium and Descemet's membrane, is derived from **neural crest cells**. - Neural crest cells migrate into the developing ocular region and differentiate into these connective tissue components of the cornea. *Neural ectoderm* - The neural ectoderm primarily gives rise to structures like the **retina**, **optic nerve**, and the posterior pigmented layer of the ciliary body and iris. - It does not contribute to the formation of the corneal stroma. *Surface ectoderm* - The surface ectoderm forms the **corneal epithelium** and the lens of the eye. - It does not give rise to the mesenchymal components of the cornea, such as the stroma. *Mesoderm* - While some mesodermal elements are involved in ocular development (e.g., extrinsic eye muscles, vascular components), the **corneal stroma** is specifically derived from neural crest cells, not general mesoderm. - The mesoderm contributes to structures like the sclera and choroid, but not directly to the corneal stroma.

Question 64: When does the basiocciput fuse with the basisphenoid?

A. 8-10 years
B. 2-4 years
C. 12-15 years
D. 5-7 years (Correct Answer)

Explanation: Note: This is a NEET-PG 2018 previous year question. The provided options and marked answer reflect the exam's original content. However, standard anatomical references indicate that the spheno-occipital synchondrosis (junction between basiocciput and basisphenoid) typically fuses between 18-25 years of age, not in early childhood. 5-7 years (Marked as correct in original exam) - This was the expected answer in the NEET-PG 2018 exam. - However, standard anatomical texts (Gray's Anatomy, Standring) indicate that spheno-occipital fusion occurs much later, typically between 18-25 years. - There may be confusion with other cranial base developments that occur in early childhood. 2-4 years - This is earlier than even the exam's intended answer. - The spheno-occipital synchondrosis remains cartilaginous at this age. 8-10 years - Still within the childhood period. - The spheno-occipital synchondrosis typically remains unfused at this age. 12-15 years - Early to mid-adolescence. - The spheno-occipital synchondrosis is usually still present, though beginning to show signs of fusion in some individuals by late adolescence. Clinical Note: The fusion of the spheno-occipital synchondrosis is an important forensic marker for age estimation, with complete fusion generally occurring by the mid-20s.

Question 65: Most common site for Cystic Hygroma is -

A. Lower third of neck (Correct Answer)
B. Overlying the parotid gland
C. Along the Zygomatic Prominence
D. Post auricular

Explanation: ***Lower third of neck*** - **Cystic hygromas** (also known as **lymphatic malformations**) most commonly occur in the **posterior triangle of the neck**, which is located in the lower lateral aspect of the neck [1]. - Approximately **75-80%** of cystic hygromas are found in the neck region, with the **posterior triangle** being the predominant site. - The **posterior jugular lymph sac** fails to connect properly with the venous system during embryonic development, leading to these cystic malformations in this characteristic location [1]. - The posterior triangle encompasses the lower lateral neck, making "lower third of neck" an acceptable description of this most common site. *Overlying the parotid gland* - While lymphatic malformations can occur in the parotid region, this represents only about **10-15%** of cases. - This is a less common site compared to the posterior triangle of the neck. - Lesions in this area might raise concern for other parotid pathologies like **pleomorphic adenoma** or **hemangioma**. *Along the Zygomatic Prominence* - This is an unusual location for a cystic hygroma, as the lymphatic drainage and embryonic development in this area are not typically associated with these malformations. - Lesions here might suggest different developmental or neoplastic etiologies such as **dermoid cysts** or **vascular malformations**. *Post auricular* - The post-auricular region is not a common site for cystic hygromas. - Swelling in this area could be due to other conditions like **mastoiditis**, **lymphadenopathy**, or **sebaceous cysts**.

Question 66: Base of sphenoid fuses with occiput at the age of -

A. 20 years (Correct Answer)
B. 30 years
C. 40 years
D. 50 years

Explanation: ***20 years*** - The **spheno-occipital synchondrosis** typically fuses by the age of **20 to 25 years**, marking the cessation of growth in the cranial base. - This fusion is an important indicator of skeletal maturity and is often used in **forensic anthropology** for age estimation. *30 years* - Fusion of the **spheno-occipital synchondrosis** beyond the early twenties is considered late and is not the typical age for this event. - By 30 years, most cranial sutures and synchondroses are already fused. *40 years* - At 40 years of age, the **spheno-occipital synchondrosis** would have been completely fused for many years, making this an incorrect age for the fusion process itself. - This age is well past the usual developmental timeframe for cranial base closure. *50 years* - Fusion at 50 years would be an **anomalous finding** as this synchondrosis is known to fuse much earlier in life. - By this age, the skull is fully mature, and fusion events of this nature have long since completed.

Question 67: Prolactin secreting gland develops from -

A. Infundibulum
B. Rathke's pouch (Correct Answer)
C. Tuber cinereum
D. 3rd ventricle

Explanation: ***Rathke's pouch*** - The **anterior pituitary gland**, which secretes prolactin [2], develops embryologically from **Rathke's pouch**. - Rathke's pouch is an **ectodermal evagination** from the roof of the primitive oral cavity (stomodeum). *Infundibulum* - The **infundibulum** is also known as the pituitary stalk, connecting the hypothalamus to the posterior pituitary [1]. - It is derived from **neuroectoderm** and forms part of the posterior pituitary, not the prolactin-secreting anterior pituitary [1]. *Tuber cinereum* - The **tuber cinereum** is a part of the **hypothalamus**. - It is involved in regulating several bodily functions but does not directly give rise to the prolactin-secreting gland. *3rd ventricle* - The **3rd ventricle** is one of the four ventricles of the brain, filled with **cerebrospinal fluid**. - It is a part of the central nervous system and is not involved in the embryological development of the pituitary gland.

Question 68: Fossa ovalis is a remnant of -

A. Septum primum (Correct Answer)
B. Septum secundum
C. Septum spurium
D. AV cushion

Explanation: ***Septum primum*** - The **fossa ovalis** is a depression in the right atrium that represents the sealed-off foramen ovale [2]. - It is formed from the **septum primum**, which becomes the floor of the fossa ovalis. *Septum secundum* - The **septum secundum** forms the limbus or rim of the fossa ovalis, not the fossa itself. - This structure develops later than the septum primum and partially covers the foramen ovale during fetal development [2]. *Septum spurium* - The **septum spurium** is an embryonic ridge in the right atrium that typically regresses during development and does not contribute to the fossa ovalis. - It is a transient structure formed by the confluence of the right and left venous valves. *AV cushion* - The **atrioventricular (AV) cushions** contribute to the formation of the AV valves and the atrial and ventricular septa, but not directly to the fossa ovalis [1]. - They are crucial for separating the atria from the ventricles and forming the mitral and tricuspid valves.

Question 69: What is the remnant of the umbilical artery?

A. Ligamentum arteriosum
B. Ligament teres
C. Ligamentum venosum
D. Medial umbilical ligament (Correct Answer)

Explanation: ***Medial umbilical ligament*** - The **umbilical arteries** (paired structures) carry deoxygenated blood from the fetus to the placenta during development [2]. - After birth, these arteries obliterate and persist as the **medial umbilical ligaments** (two in number, one on each side), extending from the internal iliac arteries to the umbilicus along the anterior abdominal wall. - The proximal portions of the umbilical arteries remain patent as the **superior vesical arteries**, which supply the bladder. *Ligamentum arteriosum* - This is the remnant of the **ductus arteriosus**, which shunted blood from the pulmonary artery to the aorta, bypassing the fetal lungs [2]. - It connects the arch of the aorta to the pulmonary artery. *Ligament teres* - Also known as the **round ligament of the liver**, this is the remnant of the **fetal umbilical vein** (a single midline structure) [1]. - The umbilical vein carried oxygenated blood from the placenta to the fetus [1], [2]. *Ligamentum venosum* - This is the fibrous remnant of the **ductus venosus**, a shunt in fetal circulation that bypassed the liver by connecting the umbilical vein to the inferior vena cava [1]. - It is located deep within the liver, forming a fissure.

Question 70: Which muscle is derived from the third pharyngeal arch?

A. Tensor tympani
B. Stylopharyngeus (Correct Answer)
C. Cricothyroid
D. Stapedius

Explanation: ***Stylopharyngeus*** - The **stylopharyngeus muscle** is uniquely derived from the **third pharyngeal arch**. - It is innervated by the **glossopharyngeal nerve (CN IX)** and plays a role in elevating the pharynx and larynx during swallowing. - This is the **only muscle** derived from the third pharyngeal arch, making it a key anatomical landmark. *Tensor tympani* - The **tensor tympani muscle** is derived from the **first pharyngeal arch**. - It is innervated by the **mandibular nerve (V3)** and dampens sound by tensing the tympanic membrane. *Cricothyroid* - The **cricothyroid muscle** is derived from the **fourth and sixth pharyngeal arches**. - It is innervated by the **external branch of the superior laryngeal nerve (CN X)** and tenses the vocal cords. *Stapedius* - The **stapedius muscle** is derived from the **second pharyngeal arch**. - It is innervated by the **facial nerve (CN VII)** and dampens sound by stabilizing the stapes bone.

Practice by Chapter

Prenatal Development

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Postnatal Growth and Development

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Age-Related Anatomical Changes

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Developmental Abnormalities

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Principles of Teratology

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Developmental Basis of Congenital Anomalies

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Molecular Aspects of Development

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Genetic Factors in Developmental Anatomy

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Environmental Influences on Development

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Clinical Aspects of Developmental Anatomy

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