48 



THE CAT. 



[CHAP. in. 



C& 



Fig. 23. VENTRAT, 



ASPECT OF THE VER- 

 TEBRAL COLUMN. 



c. Cervical, 



(L Dorsal, 



I. Lumbar, 



s. Sacral, and 



cci. Caudal vertebra. 



the dorsal and lumbar vertebrae together form 

 a curve which is much more strongly convex 

 upwards than the preceding curve is convex 

 downwards. The neural spines (which are longest 

 in the dorsal vertebrae) change their direction at 

 about the middle of the posterior curve, that of 

 the tenth dorsal vertebra inclining backwards, 

 and that of the eleventh forwards, their junction 

 indicating the centre of motion. 



The breadth of the ventral part of the back- 

 bone (i.e. the transverse diameter of the vertebral 

 centra), narrows slightly from the axis to the first 

 dorsal vertebra ; it remains much the same to 

 about the fifth, and then gradually widens to the 

 first sacral, whence it again decreases rapidly 

 to the beginning of the tail, and then very 

 gradually to the end of that organ. The width 

 of the column, including the transverse pro- 

 cesses and the lateral masses of the sacrum, is 

 at its maximum at once at the atlas, and sud- 

 denly decreasing at the axis. It thence remains 

 much the same, but gradually broadens to the 

 first dorsal, whence it again very gradually 

 narrows to the last dorsal vertebra. Thence it at 

 once increases rapidly to the last lumbar vertebra, 

 which is about as wide as is the atlas. Thence 

 backwards the spine gradually narrows to the end 

 of the vertebral series. 



The ventral surface of the vertebral column 

 bears no median prominence save the slight 

 longitudinal one beneath the centrum of the axis, 

 and of certain lumbar vertebrae, together with the 

 tubercles of the atlas and of some caudal vertebrae 

 and the chevron bones. The dorsal surface bears a 

 median series of spines, which are longest in the 

 anterior dorsal and lumbar vertebrae. They are 

 variously directed, as has been already described. 



On each side of the series of spinous processes 

 are the neural laminae forming the bottom of the 

 "vertebral grooves," each of which is bounded ex- 

 ternally by the transverse, zygapophysial and 

 metapophysial processes, and internally by the 

 spinous processes. Each groove is broad and 

 shallow in the neck, and deeper and narrower 

 in the anterior thoracic region, and deepest of 

 all at the lumbar region. The laminae overlap in 

 the neck and in the anterior and middle part of 

 the dorsal region. They leave an open space 

 between them in the lumbar portion of the ver- 

 tebral column. 



