54 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



(1) The body of the hyoid is the flat plate of cartilage in the floor of the buccal 

 cavity. Its concave anterior margin receives the base of the tongue. Its 

 lateral anterior corners have short alary processes, and its posterior corners 

 poster o-lateral processes. 



(2) The anterior horns or cornua of the hyoid are the long, slender rods which 

 curve back from the anterior margin of the body to the pro-otic bones of the 

 skull. 



(3) The thyroid processes or posterior horns are the two processes which 

 diverge from the posterior margin inclosing the laryngeal chamber between them. 

 They are ossified while the other parts of the hyoid are cartilaginous. 



(4) The columella, the small slender bone in the middle ear, one end of which 

 is attached near the middle of the tympanic membrane, is probably a part of the 

 hyoid apparatus. 



4. Bones of the pectoral girdle (Holmes, p. 238). The pectoral girdle forms 

 a bony arch for the support of the fore limbs. It is incomplete dorsally and has 

 no connection with the vertebral column. Ventrally its two halves are united 

 by the interposition of the sternum. Each half of the girdle consists of: 



a) Suprascapula, the most dorsal bone, large and flat with a cartilage along 

 its free dorsal border. 



b) Scapula, the bone ventral to the preceding and containing a cup-shaped 

 cavity, the glenoid fossa, in which the long bone of the upper arm is inserted. 



c) Clavicle, the anterior bone of the two which compose the ventral aspect 

 of the girdle. It is a membrane bone, the only one in the skeleton outside of the 

 skull and jaws. 



d) Procoracoid, the cartilage which is covered over by the clavicle and which 

 fails to ossify because its function is usurped by the clavicle. 



e) Coracoid, the posterior of the two ventral bones. It takes part in the 

 glenoid fossa. 



5. The sternum (Holmes, p. 240). The sternum is a chain of bones and 

 cartilages between the two ventral ends of the halves of the pectoral girdle. 



a) Episternum, the rounded catilage forming the anterior extremity of the 

 sternum. 



b) Omosternum, the bone behind the preceding. 



c) Epicoracoids, the cartilages between the medial ends of the coracoid bones. 



d) Sternum proper or mesosternum, bony rod behind the coracoids. 



e) Xiphisternum, terminal rounded cartilage. 



6. Bones of the pelvic girdle (Holmes, pp. 242-43). This is the bony girdle 

 which supports the hind limbs. It is complete dorsally, forming a joint with the 

 transverse processes of the last vertebra. The bones of each half of the pelvic 

 girdle are: 



a) Ilium, the long scythe-shaped dorsal bone which extends forward parallel 

 to the urostyle to articulate with the transverse processes of the sacral vertebra. 



