The foramina of Monro form the communication between the lateral ventricles and the third ventricle. The cerebral aqueduct of Sylvius flows caudally into the fourth ventricle (choice A). The lateral foramina of Luschka and the median foramen of Magendie allow for communication between the fourth ventricle and the subarachnoid space. The third ventricle communicates posteriorly with the cerebral aqueduct of Sylvius (choice D). Thus, the third and fourth ventricle communicate by way of this cerebral aqueduct.

66) During development, the notochord grows in a cranial direction until it reaches the prechordal plate. This plate is the primordium of the oropharyngeal (or buccopharyngeal) membrane, which, in the embryo, will separate the stomodeum from the foregut. At 26 days of gestation, the oropharyngeal membrane will break down, allowing communication of the foregut with the oral cavity. Of the following structures in the adult, which one lies at the same location as the embryonic oropharyngeal membrane?

The palatoglossus muscle, which can be observed in the oral cavity to form the palatoglossal arch anterior to the palatine tonsil, lies in the same location as the embryonic oropharyngeal membrane. It lies at the junction line between the stomodeum and the foregut. The buccinator (choice A) is a muscle of the cheek and thus is located in the original stomodeum. The palatopharyngeus (choice C) is located posterior to the palatoglossus and palatine tonsil, forming the palatopharyngeal arch. The palatopharyngeus, stylopharyngeus (choice D), and superior constrictor (choice E) muscles are all pharyngeal muscles and thus are located in the original foregut.

67) In the skull, a network of thick-walled vessels named dural venous sinuses drains the cerebrospinal fluid and the venous blood from the brain. These vessels are formed by reflections of the dura mater, which also form partitions between major parts of the brain. Which of the following dural venous sinuses is associated with the falx cerebri?

The falx cerebri is the dural partition separating the hemispheres of the brain, above the corpus callosum. It has in its superior edge the superior sagittal sinus and in its inferior border, the inferior sagittal sinus. The cavernous sinus (choice A) is a dural pocket in the middle cranial fossa and is located on either side of the sella turcica. It is unusual because it contains the internal carotid artery and cranial nerves III, IV, V1, V2, and VI. The sigmoid sinus (choice C) is located in the posterior cranial fossa, below the level of the tentorium cerebelli, which contains in its posterior border the transverse sinus (choice E).

In the fetus, the umbilical vein connects directly to the ductus venosus, a fetal vessel which bypasses the liver to bring oxygenated blood to the inferior vena cava (choice D). The descending aorta (choice A) distributes blood to the body and, in the fetal circulation, brings blood to the umbilical arteries by way of the iliac arteries for return to the placenta for oxygenation. The ductus arteriosus (choice B) is a fetal vessel which allows bypass of the oxygenated blood from the pulmonary trunk to the arch of the aorta. The portal vein (choice E) is formed by the union of the splenic vein and the superior mesenteric vein; it returns blood from the digestive system to the liver.

70) A patient was thrown from a tractor, which partially ran over him and caused injury to the base of the skull. The origin of the internal jugular vein at the jugular foramen was compromised. Which of the following cranial nerves courses through the jugular foramen?

70)
The spinal accessory (eleventh cranial) nerve takes its origins in the neck, but then runs cranially into the skull through the foramen magnum to join with its cranial component. They exit as one through the jugular foramen, along with the glossopharyngeal (ninth cranial) and vagus (tenth cranial) nerves. The abducens (sixth cranial) nerve (choice A) runs through the superior orbital fissure to reach the orbit. The facial (seventh cranial; choice B) and vestibulocochlear (eighth cranial; choice E) nerves run together through the internal acoustic meatus into the temporal bone. The facial nerve exits the skull through the stylomastoid foramen. The hypoglossal (twelfth cranial; choice C) nerve exits the skull through the hypoglossal canal.

71) Protein zero (P0 ) is the predominant protein in myelin in the peripheral nervous system and its function is to stabilize adjacent plasma membranes by interaction with similar P0 molecules. Which of the following cells manufacture P0 ?

71) Schwann cells produce myelin in the peripheral nervous system whereas oligodendrocytes produce myelin in the central nervous system. Oligodendrocytes manufacture the proteolipid protein, the functional equivalent to P0 in the central nervous system. Fibrous (choice A) and protoplasmic (choice D) astrocytes are supportive cells which play a role in the regulation of brain metabolism. Microglia (choice B) are mesodermal in origin and have phagocytotic activity in the central nervous system.

72) A perilunate fracture dislocation is a devastating closed injury of the wrist. It usually results from a fall where the weight of the body is transferred onto the wrist. The hand is caught in the hyperextended and ulnar deviated position. The fracture dislocation involves rupture of interosseous ligaments, joints, and ultimately dislocation/fracture of the lunate bone. In the anatomical position, which carpal bone lies directly distal to the lunate?

72)
The capitate bone lies directly distal to the lunate. The mechanism of perilunate fracture dislocation involves rupture of the radioscaphocapitate and scapholunate interosseous ligaments, dislocation of the capitolunate joint, rupture of the lunotriquetral interosseous ligament, and finally dislocation/rupture of the lunate. In the anatomical position, the hamate (choice B) is the most medial carpal bone, located just distal to the triquetrum. The scaphoid (choice C) lies lateral to the lunate and proximal to the trapezium (choice D), the carpal bone articulating with the thumb. The trapezoid (choice E) is medial to the trapezoid and distal to the scaphoid. The lunate bone (choice C) lies adjacent to the scaphoid in the proximal row of carpals and with the scaphoid articulates with the radius at the radiocarpal or wrist joint. It is not related to the anatomic snuffbox. The pisiform bone (choice D) is a sesamoid bone in the tendon of the flexor carpi ulnaris on the lateral wrist. It is not related to the anatomic snuffbox.

73) A 19-year-old man was in a barroom brawl and was punched squarely in the right eye. He comes to the emergency room the next day and complains of diplopia. An X-ray reveals fracture of the orbital floor. Neurological examination shows loss of sensation of the skin of the right face below the right eye and the upper gums. Which of the following nerves may be injured?