COMPARATIVE ANATOMY 25 



i. The foramen ovale lies immediately posterior to the fora- 

 men rotundum. It also carries a branch of the fifth nerve. 



j. The stylomastoid foramen is a small opening posterior to 

 the external auditory meatus for the passage of the seventh 

 cranial nerve. The shallow groove ventral to this foramen is 

 for the attachment of the hyoid bone. 



k. Eustachian tube. At the anterior end of the tympanic 

 bulla is a foramen which connects with the cavity of the middle 

 ear within the bulla. It serves for the passage of the Eustachian 

 tube from the middle ear to the pharynx. 



1. The jugular foramen is an opening near the posterior end 

 of the bulla and serves for the passage of the ninth, tenth, and 

 eleventh cranial nerves and the jugular vein. 



m. The hypoglossal canal may be seen by looking into the 

 foramen magnum on either side. The canal makes its exit 

 near the jugular foramen. It carries the twelfth cranial nerve. 



n. Internal auditory meatus. Examination of the internal 

 surface of a separate temporal bone reveals two prominent 

 openings. The larger one, anterior to the petrous region, is 

 for the passage of the Eustachian tube, already mentioned. 

 The other, consisting of a deep pit in the center of the petrous 

 region, is the internal auditory meatus. The seventh and eighth 

 cranial nerves enter it. The seventh emerges through the 

 stylomastoid foramen; the eighth (auditory) passes to the inner 

 ear by means of several foramina in the bottom of the pit. 



Examine a skull bisected longitudinally and one with the 

 top of the cranium removed. Identify the various parts. 

 Skulls of different mammals are available in the laboratory for 

 those who wish to compare them with the cat. 



Larynx. — Study the model of the human larynx. The 

 U-shaped structure at the top is the hyoid bone which serves 

 as a support for the tongue. The largest cartilage of the larynx 

 is the thyroid cartilage, which gives the shape to the voice box. 

 From the notch in the anterior of the thyroid cartilage extends 

 the epiglottis, which during the act of swallowing, covers over 

 the opening into the larynx and prevents food entering. The 

 two small cartilages to which one end of each vocal cord is 

 attached are the arytenoids. The arytenoid cartilages rest on 

 the cricoid cartilage, which is shaped somewhat like a signet ring. 

 Changes in position of the cricoid and arytenoids with respect 



