NECTURtJS MACULATUS. 395 



with the longitudinal axis of the vertebra. From there as far as S, it is gradually smaller 

 and more depressed. After S it becomes again larger and more erect, so that the spine of 

 21 is about equal to that of 3, and that of 22 surpasses it. It rapidly lengthens as far as 

 26 to 27, where it reaches its maximum of length and is about equal to the haemal spine; 

 from then on, both neural and haemal spines become gradually reduced as the vertebrae 

 diminish in size. 



A haemal spine appears suddenly on the 22d to 24th vertebra, usually the 23d, an 

 indication of it sometimes being found upon the previous vertebra in the form of a thin 

 bony bi'idge which stretches across the ventral face of tlie vertebra from the outer angle 

 of the transverse process to the centrum, thus covering the posterior portion of the ven- 

 tral lamina. In one case noted, the vertebra just anterior to H bore upon one side a 

 slender process, 4 to 5 mm. long, evidently representing an incomplete haemal arch. 

 The first haemal .spine is of about tlie maximum size, and, after three or four vertebrae 

 in which this size is maintained, the haemal spines begin to diminish with the gradual 

 reduction of the vertel)i'ae, as in the case of the neural spines. The neural and haemal 

 spines of the same vertebrae closely resemble one another, but, in the first few vertebrae 

 that possess both, the former take a slightly more erect position while the latter lie more 

 nearl}- parallel to the axis of the vertebrae. Towards the end of the tail both neural and 

 haemal spines sometimes appear Ijifurcated at the tip, or even double as far as their base. 

 In a given vertebra this may affect either spine alone or botli spines. 



Zygajwp/u/ses. — In 1, the anterior z3'gapophyses are wanting and the posterior are 

 near together. From 2 to S both sets are divergent and almost identical, save that the 

 entire vertebrae at about 15 to 17 are a little wider than elsewhere and hence the 

 zygapophyses are here farther apart. After S the vertebrae ra^^idly become narrow, and, 

 beginning with H, both sets approach very near together and are reduced in size. They 

 become obsolete at about 26, beyond which the vertebrae articulate solely by means of 

 the vertebral centra. 



Ventral foramina. — These do not appear in the three anterior vertebrae and are 

 usually of small size in 4. From then on, as far as H, there is usually a pair in each 

 vertebra, although occasionally the foramen of one side may be converted into a notch 

 by a deficiency in the ventral lamina. In H, where the roots of the haemal spine form 

 thin laminae lying over the region of these foramina, openings occur not only in the ven- 

 tral laminae as usual, Init also in the laminae connected with the haemal spine, and the 

 two sets of foramina are accurately superimposed. Beyond H the reduction of the entire 

 transverse process renders the ventral foramina unnecessary, but in the two or three 

 vertebrae succeeding H the new foramina through the base of tlie haemal spine may be 

 present, although usually appearing upon but one side. 



