SKELETON 



6l 



The haemaphophysial ribs end freely below, never being connected with a 

 sternum. In some aberrant fishes they are lacking, while in the ostariophysi 

 they play a part in the 'Weberian apparatus' connecting the swim bladder with 

 the ear (p. 269). The teleosts have, in addition, numerous rib-like structures 

 which are not preformed- in cartilage (epinetirals, epipleurals) scattered among 

 the muscles; these are formed in the epaxial or hypaxial myosepta or in the 

 horizontal partition. 



Fig. 58. — Diagrams of vertebra; of Lamargus, based on Schauinsland, to illustrate 

 his view of the homologies of the two types of ribs. A, mid caudal; B, base of tail; C, 

 middle of trunk; Z>. cervical region, c, centrum; h, haemal process; na, cranial neural 

 arch; nc, notochord; np, caudal neural arch; p, hasmal arch or haemapophysis; r, rib. 



Typically, the true rib (it is not certain whether this is the primi- 

 tive form) has two heads for articulation with the vertebra, a 

 capitular head connecting with the parapophysis, a tubercular 

 head joining the diapophysis. Between the two heads and the 

 centrum is a space, the vertebrarterial canal, through which the 



y^^ 



I- iG. SQ. — Front and side views of cervical vertebra of fowl, showing the cervical rib. 

 Cf centrum; cs, spinal canal; d, diapophysis; p, parapophysis; r, rib; va, vertebrarterial 

 canal; the arrow in the side view passes through the canal 



vertebral artery passes (fig. 41, C). The true ribs, which are pre- 

 formed in cartilage, have various extents in the diflferent regions of 

 the body. In the thoracic region, where they have the greatest 

 extension, the ribs have to allow for changes in size of the contained 

 cavity, and hence parts of them are frequently left unossified, or 

 at least they are jointed, the two parts being called vertebral and 

 sternal ribs (fig. 60, vr, sr). 



