MUSEUM OF comparatrt; zoology. 13 



section shows so much uniformity of appearance that it is only by means 

 of the hypophyses, or external marks, that the segments can be detected 

 (fig. 2). In the neural canal (nc) and between the interneurals {in) 

 the segments are tolerably distinct. With the exception of a small lump 

 in the mouth of the nerve aperture (fig. 5), there is no evidence of cal- 

 cification in the vertebrae of more than half of the total. Both neurapo- 

 physes and interneurals are perforated for the nerves. The interneurals 

 are rather thick and strong. Small wedge-shaped interspinous pro- 

 cesses (is) extend about half-way through the crest. The ridge formed 

 by the interneurals and the interspinous processes is surmounted by a 

 very strong elastic cord of fibrous tissue. Over the abdominal cavity 

 the hsemal processes bear short flexible unsegmented ribs, and be- 

 tween the hsemapophyses are the small triangular interhsemals (ih). 

 Above the anterior portion of the anal fin the haemapophyses begin to 

 take on a downward extension, gradually becoming blade-like, and over 

 the posterior portion of the same fin they are supplemented by small 

 pieces of cartilage (PI. XIII. c-c), which farther back become the ra- 

 dials of the caudal. The radials of the upper part of the caudal begin 

 independently, or separate from the vertebrae; farther back they join 

 the latter and continue to the end as if part of the column. The lines 

 of separation between the vertebrae and accessory cartilages are very 

 indistinct ; in places, it is only with diflBculty they can be traced. The 

 column ends abruptly ; the terminal segment resembles a slice taken 

 from the front of a following vertebra. The canals are visible at the 

 end, but seem to be stopped by soft cartilage. 



The anterior vertebrae of a large Heptabranchias at hand differ from 

 the anterior of those described above in having the notochord segmented 

 by thick membranous septa, each of which has a very small central 

 perforation. Towards the tail there are vertebz'al constrictions, and the 

 column tapers to a point. 



Th^ Pectoral Cartilages, 



Plate XI. 



Coraco-scapulars, fig. 2. — These are strong, moderately slender, and 

 taper to a point at each end. The coracoid is irregularly triangular, 

 flattened below, broadened backward, and in the anterior third of its 

 length — which is turned upward, like the runner of a sled, toward the 

 binder basibranchial — tapers to a point. The bent portions are an inch 

 in length and nearly straight on their lower faces. They are applied to 



