596 OSTEOLOGY OF LAKID^. 



The above table differs from those given by Owen, Totld's Cyclop. Auat. and Phvs., 

 Art. Aces, andbyEYTOX, Osteol. ATium. Prof. Owen's figures are : " Ciitai-ractes." lo — 

 9— 13— t-; "aull" IS— Ji^ll— 5^; " Tmi," 14— !?— 10— ?. "Mr. Ey ton gives: Larus ridi- 

 linidns. 14 — 7 — 1-2 — 7; S/friia arctica, 13 — li — V2 — li; ifAj/wcAops liiffCfl, 13 — 6 — 12 — S. It 

 is to be expected that discrepant statements should occur in the enumeration of the 

 sacral vertebrie, as the composition of that most complex of all bones is difficult to 

 interpret. In the other instances we may presume that there is actually a variation 

 with the species in number, of vert^bne of tlie several regions. I give the numbers as 

 determined by myself in the specimens of the three species above mentioned, adding 

 the formula; of Owen and Eyton for comparison. 



The peculiarities of the several regions, and of the difl'ereut vertebrie composing 

 them, may be briefly noticed : 



Cervical ^"EKTebr^. — The alias is little more than a simple ring, its foramen slightly 

 flattened inferiorly. Its '' body '' is merely a slight projection on the inferior edge of its 

 circumference ; bearing, cephalad, a perfectly circulsir facet for articulation with the 

 occipital condyle; and caudad, and ujion its superior margin, a deep longitudinal 

 channel, so deep as almost to amount to a canal for the reception and retention of the 

 axial odontoid process. Superiorly on each side are indications of transveree pro- 

 cesses; inferiorly there is the rudiment of a " ventral spine," 



Axis,— ^This is of a somewhat peculiar shape. The spinous and transverse processes, 

 both of which are quite well developed, seem to lie considerably posterior to the 

 body of the vertebra, in consequence of an obliquity backward of the neural arch 

 from the centrnm. The ventral spine is well developed, thin, with an anteriorly con- 

 vex, posteriorly concave margin ; oblique in duectiou, projecting backward as well as 

 downward. The body of the vertebra proper consists of little more than a base for 

 the support of the odontoid process, which latter is acute, well developed, semicylin- 

 drical, its surface toward the spinal canal being flattened. The transverse articulating 

 facets are small, subcircular, slightly concave, situated beneath the processes, at their 

 bases. The other articulation is elongated, compressed, vertically concave, hori- 

 zontally convex. The motion between the atlas and the third vertebra is very free iu 

 a vertical direction, less so in a horizontal, while rotation is greatly restricted. 



The third and fourth vertebra? somewhat resemble the axis in having a broad, thin, 

 longitudinal lamina of bone extending between the anterior and posterior articular 

 processes. They are also very short and broad. The other vertebra> all diftev some- 

 what, but the difference is so gradual that they may most conveniently be described 

 collectively, Tlie lowest or doi'sad vertebrie are the largest and broadest, but com- 

 paratively the shortest. Their posterior articular processes are short and slightly 

 divaricating; as we proceed up the neck they become longer, more attenuated, and 

 more widely diverging. This attennation is greatest on about the fifth vertebra. 

 The transverse processes are very wide below, and extend directly outward from the 

 median line. Further up the neck they are less px-ominont, and have also an anterior 

 obliquity. This process on the last vertebra does not form a canal for the passage of 

 the artery; the canal commences on the twelfth, as a simple foramen, becoming nar- 

 rower in diameter, but at the same time more and more lengthened and caual-like, up 

 to the atlas. 



Superior spinous processes, or the "neural spines," are well developed on the first 

 five vertebra?, but they diminish in size from the third to the sixth, when they become 

 quite obsolete, and do not reappear. Inferior or ventral siiinous processes are found 

 very well developed on the first four vertebra', being largest on the atliis ; they then 

 entirely disappear, and are not found again until about the eleventh vertebra, where 

 they are slightly elevated, longitudinal, vertical lamella". Styloid jirocesses are found 

 thronghout the whole length of this portion of the spine, except the atlas and axis, 

 and, usually, the last vertebra. They commence on the third vertebra, elongate on 

 each successively to the sixth or seventh, where they are longest and thinnest, meas- 

 uring two-thirds the length of the body of the vertebra. They then regularly grow 

 shorter and more obtuse till they are hardly perceptible on the thirteenth and quite 

 obsolete on the fourteenth or last cervical. 



Air is admitted into the vertebra; by numerous foramina on the sides of the bodies, 

 about the roots of the transverse processes and in the canal for the artery. 



There is the ordinary difference iu the calibre of the spinal canal iu the centre and 

 at the extremities of each vertebra. The planes of the articular surface are, as usual, 

 so disposed as to produce, iu the most natural position of the head and neck, the ordi- 

 nary sigmoid flexure, When the neck is extended there is on the doraal surface a 

 large diamond-shaped space between each vertebra and the next covered in only by 

 ligamentous tissue. 



DouSAL VEETEBRJE, — If we regard the presence of a rib as characteristic of the ver- 

 tebra' of this region of the spine, wo shall have eight as the total number of dorsal 

 vertebra', Bnt the two last of these are perfectly consolidated with and continuous 

 T,ilh (he first sacral; and their transverse and spinous processes also have a lateral 

 -ai:<l superior auchylosis with the iliac bones. At the same time there is a perfect artio- 



