56 



LECTURE III. 



Cuvier appears to have overlooked the peripheral longitudinal 

 lamellje: he says, "dans certains grands squales, le maximus, par ex- 

 ample, ce sont des lames cylindriques, toutes concentriques, toutes 

 separees par des couches d'un cartilage tendre," &c. {Legons (TAnat. 

 Comj). 1835, i. p. 127.) Our compilers have copied this description, 

 and, as usual, have applied it to the vertebrae of Fishes in general. 

 In the Squatina, the part of the vertebral body included by the ter- 

 minal cones is, indeed, composed of concentric layers, decreasing in 

 breadth as they aj^proach the centre ; but, in the Cestracion, there 

 are no concentric layers, but only longitudinal lamellae, radiating 

 from the centre to the circumference, and giving off short lateral 

 plates as they divei'ge : the most common disposition of the osseous 

 matter in the vertebral bodies of the Plagiostomes is a combination 

 of longitudinal and cylindrical plates, as in the Selache. 



In the Tope {Galeus communis), as well as in most Sharks which 

 possess the nictitating eyelid, may be seen the highest stage of ver- 

 tebral ossification in the Chondropterygian Fishes : the external 

 surface, as well as the terminal concavities, of the centrum, are 

 covered by a smooth osseous crust, except at the openings of the 

 four conical cavities, which, as in Selache, correspond with the 

 bases of the neur- and j^ar-apophyses. In most Sharks the principle 

 of vegetative repetition is manifested in the numerous centres of os- 

 sification in the cartilaginous neural and haemal arches : four stellate 

 points, for example, represent the neurapophysis in Galeus, and as 

 many smaller points the neural spine : in most other Squalian genera 

 the centrum supports two osseous pieces on each side of the spinal 

 canal : one of these, by its position above the neural canal of the 

 centrum, claims to be regarded as the neurapophysis ; the other by 

 its position, usually over the intervertebral space, and by its shape 

 as an inverted cone, indicates an intercalary interneural piece. It is 

 worthy of remark that the nerve-foramen is usually not a " trou de 

 conjugaison" between these cartilages, but a direct perforation of 

 either the neurapophysis, or of both this and the interneurapophysis, 

 when both roots of the spinal nerve escape separately. The ribs 

 (pleurapophyses) are short and simple semi-osseous styles attached to 

 the ends of the parapophyses, in this skeleton of the Tope, [Prep. 

 369.] along the twenty-six anterior vertebras, decreasing in length 

 posteriorly. In the Piked Dog-fish the ribs are quite cartilaginous, 

 and I have counted forty pairs : in a few Sharks, as in Carcharias, 

 Heptanchus, and Alopias, the ribs ai'e connected to the centrum at 

 the base of the parapophyses. 



In the Monk-fish (^Squatina), a transitional form between Rays 

 and Sharks, the vertebral bodies are very numerous, and manifest ex- 



