So 



LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



ischium 

 pubis 



fibulare 

 centralia 



girdle is the straight or slightly curved bar of cartilage placed across the ventral 

 side at the end of the trunk region between the anterior ends of the pelvic fins. 

 This bar is called the ischiopubic bar and represents a primitive unossified pelvic 

 girdle. In many elasmobranchs (including the dogfish) the two ends of the bar 

 bear slight processes projecting outward ; these are the iliac processes. 



Attached to the pelvic girdle, articulating to it at the base of the iliac pro- 

 cesses, are the pelvic fins. The skeleton of the basal part of the fins, which is 



imbedded in the body wall, consists of a num- 

 ber of cartilaginous pieces, the cartilaginous fin 

 rays; the skeleton of the free external part of the 

 fin is composed of a number of slender parallel 

 dermal fin rays. As the latter are part of the 

 exoskeleton, they will not be considered further. 

 The cartilaginous fin rays are arranged in two 

 series, a medial series, consisting of one or two 

 (in some forms three or five) much enlarged carti- 

 lages, and a lateral or outer series, composed of 

 a number of small cartilages disposed in one or 

 more rows. The inner series of fin rays are called 

 basalia or basals, the outer series, radialia or 

 radials. There is usually present a single basal, 

 the metapterygium, an elongated curved cartilage 

 forming the whole medial border of the fin, but 

 in some forms there is an additional basal, the 

 propterygium, situated at the anterior end of the 

 metapterygium. The radials usually consist of a 

 row of rod-shaped cartilages, their long axes at 

 right angles to the axis of the metapterygium. 

 In male specimens the posterior radial is greatly enlarged to form the cartilage 

 of the clasper. The basals have probably arisen through the fusion of a number 

 of smaller cartilages. 



Draw the pelvic girdle and fin of an elasmobranch. 



3. The pelvic girdle and hind limb of urodeles.— Study these parts in dried 

 or preferably preserved specimens of Necturus or Cryptobranchus. The urodele 

 girdle is in a condition intermediate between the cartilaginous girdle of elasmo- 

 branchs and the bony girdle of reptiles. It is situated on the ventral side at the 

 end of the trunk between the hind limbs. Its ventral portion has the form of a 

 flattened plate, which may be designated the ischiopubic plate or pelvic plate. The 

 anterior part of this plate is cartilaginous and is called the pubic cartilage. In the 

 posterior part of the plate a pair of opaque (i.e., bony), rounded areas may be 

 seen. Each of these areas is a bone, the ischium, which, as already explained is 

 the posterior ventral bone of typical girdles. The ischia are produced by ossifi- 

 cation in the pelvic plate. From each side of the pelvic plate a rod of bone extends 



Fig. 24. — Diagram of the bones 

 of the typical pelvic girdle and hind 

 limb. (From Parker and Haswell's 

 Textbook of Zoology, courtesy of the 

 Macmillan Company.) 



