PISCES. 



965 



fig. 498. 



vertebrae of the spine by a loose ligamento- 

 cellular substance. 



In other Sharks and in the Rays (Jig. 496, 

 1, 2, 3, 4, and Jig. 500, 3, 4, 5) the ossification 

 of these pieces is very imperfect ; the branchiae, 

 in the latter more 

 especially, being al- 

 most entirely sustain- 

 ed by membranous 

 structures. 



The pharyngeal 

 bones in the true 

 Chondropterygii are 

 totally wanting. 



In some Sharks, 

 as, for example, in 

 Galeus, there are ves- 

 tiges of a true sternum 

 situated below the 

 branchial apparatus, 

 from the anterior edge 

 of which it is sus- 

 pended by ligamen- 

 tous attachments, 

 while posteriorly it is 

 connected with the 

 centre of the zone, to 

 which the pectoral 

 fins are attached. To 

 the sides of this ster- 

 num are appended 

 five or six pairs of 

 sternal ribs, but the 

 ossification of these 

 bones, as well as of 

 the sternum itself, is 

 very incomplete. 



The vertebral co- 

 lumn of the cartilagi- 

 nous Fishes presents 

 two or three very 

 remarkable peculiari- 

 ties. In the Kay-tribe 

 (Jig. 500, 6) all the 

 vertebrae of the ante- 

 rior portion of the 

 spine for a considera- 

 ble distance are im- 

 moveably fixed toge- 

 ther by an incrusta- 

 tion of earthy matter 

 that forms a kind of 

 tube or sheath in 

 which they are en- 

 cased, the number of 

 vertebrae thus anchy- 

 losed to each other be- 

 ing only indicated by 

 the foramina through 

 which the spinal 

 nerves make their es- 

 cape. 



Another peculiari- 

 ty is that both in the 

 Sharks and Rays 

 there are twice as 

 many superior verte- skeleton of Sturgeon (Acci- 

 bral laminae as there pen ser Sturio). 



Iffr 



are vertebra. This is owing to the develope- 

 ment of spinal laminae to cover the interverte- 

 bral spaces, in addition to those which constitute 

 the spinal canal in other vertebrata. 



To the transverse processes of the vertebrae 

 covering the abdomen rudiments of dorsal ribs 

 are appended. In the Raidae, however, these 

 are very small ; but in Sharks, (Jig. 496, m,) 

 and more especially in the Sturgeons (Jig.4Q9, 

 b, c,) they attain considerable dimensions. 



Along the whole length of the post-abdo- 

 minal region of the vertebral column there 

 are developed haemapophysial arches and infe- 

 rior spinous processes, but the latter are always 

 exceedingly short and imperfectly formed. This 

 is well seen in the Sturgeon (fig. 498), in 

 which fish, although the central portion of the 

 vertebral column remains permanently cartila- 

 ginous, the haemapophysial arches and spines 

 are distinctly bony. 



There are no interspinous bones, the dorsal 

 and anal fins being only connected to the 

 spinous processes of the vertebrae by broad 

 ligamentous expansions. The structure of the 

 caudal fin is likewise very different from what 

 is met with in the osseous Fishes. In the Sharks 

 and Sturgeons, (fig. 498,) which have the tail 

 deeply furcate, the vertebral column is conti- 

 nued into the upper portion along its entire 

 length, the caudal fin being entirely supported 

 by long rays connected both superiorly and 

 inferiorly to the extremities of the spinous 

 processes of the individual vertebrae. 



The framework to which the anterior extre- 

 mities or pectoral fins are attached is a strong 

 osseous zone which encircles the body imme- 

 diately behind the branchial apparatus. This 

 zone consists superiorly of the scapular and 

 supra-scapular pieces, and inferiorly of a broad 

 osseous belt (Jig. 497, A",) which encloses the 

 fore part of the abdominal cavity, representing 

 the coracoid and clavicular apparatus of the 

 Reptilia. In the Raidse the supra-scapular 

 pieces are inseparably connected with the 

 spinous processes of the dorsal vertebrae, but 

 in the different races of Sharks they are loose 

 and unattached. At the junction between the 

 dorsal and abdominal portions of the above 

 zone are attached by strong articulations the 

 pieces which support the rays of the pectoral 

 fin. These pieces represent the whole brachial 

 and carpal apparatus of the higher Vertebrata. 

 In the Rays these are of enormous dimen- 

 sions, (Jig. 500, 8, 9, 10, 11 J extending pos- 

 teriorly so as almost entirely to surround the 

 cavity of the abdomen, whilst anteriorly they 

 are prolonged in a similar manner in front 

 of the cranium. To the external aspect of this 

 vast carpus are attached upwards of a hundred 

 fingers supporting the enormous pectoral fins, 

 which here form by far the greater portion of 

 the body, giving it that square shape for which 

 these Fishes are so remarkable. Towards the 

 circumference of the body each of the fin-rays 

 bifurcates (12), so that the total number of 

 phalanges entering into the composition of this 

 prodigious hand is one of the most remarkable 

 iacts in comparative osteology. 



