20 GUIDES FOR VERTEBRATE DISSECTION 



the middle of the inner surface and a large angular bone making 

 up most of the inner surface. Between these bones runs Meckel's 

 cartilage, its posterior end enlarged for articulation with the 

 quadrate. (In many vertebrates this end ossifies as an articular 

 bone.) 



Draw the lower jaw from the inner and outer surfaces. 



The rest of the visceral skeleton is composed of a series of 

 cartilage arches in the floor of the mouth and throat. These 

 arches, of which there are four, are connected together by a 

 longitudinal median portion, the copula. The most anterior 

 arch is the hyoid, each half of which is composed of a small medial 

 hypohyal and a larger and more lateral ceratohyal. The copula 

 between the hyoid and the next (the first branchial) arch is the 

 first basibranchial. Each half of the first branchial arch is 

 composed of a ceratobranchial next the middle line, and a larger 

 distal epibranchial. Branchial arches 2 and 3 are more incom- 

 plete, the ceratobranchial elements being small or absent. Be- 

 hind the first ceratobranchials the copula is continued by a 

 slender bone, the second basibranchial. 



Draw this hyoid-branchial apparatus. 



The pectoral, or shoulder girdle, is that arch of cartilage and 

 bone which supports the fore limbs. Its two halves are not 

 connected, but overlap ventrally. Each half consists of dorsal and 

 ventral portions. In the ventral portion, which is entirely car- 

 tilaginous, distinct elements cannot be recognized but merely 

 regions, a procoracoid in front, a coracoid behind, the limits 

 between the two being slightly indicated by a small opening, the 

 coracoid foramen, passing through the cartilage and by the pit, 

 the glenoid fossa, by which the arm is articulated to the girdle. 

 The dorsal half of the girdle consists of a bony element, the 

 scapula, continued dorsally by a larger cartilaginous plate, the 

 suprascapula. 



The bone of the upper arm (humerus) is cartilaginous at 

 either end, but has a bony shaft. On the lower surface it presents 

 a strong crista deltoidea for the attachment of the thoracic 

 muscles. In the forearm are two bones, the radius on the thumb 

 or anterior side, the ulna on the other; both have cartilaginous 

 ends, the proximal of the ulna extending beyond the elbow- 

 joint as a strong olecranon process. 



In the wrist (carpus) then- are six or seven cartilages arranged 



