386 Dr. Otto 31. Reis — Structure of Squaloraja and Chuncera. 



interesting fragments of the frontal spine and rostrum of Squaloraja, 

 duplicate specimens from the British Museum, kindly lent to the 

 present writer for study by Dr. Henry Woodward, Keeper of the 

 Geological Department. 



The fragment of a frontal spine shown from the ventral aspect 

 in PI. XII, Fig. 4, exhibits at the proximal end some interesting 

 features, which were revealed on extrication from the enveloping 

 matrix. The expanded proximal end is small, of triangular shape, 

 and slightly excavated on the ventral side, this excavation being 

 subdivided by a little median crest. As long ago supposed by 

 W. Davies, this feature indicates the insertion of two muscles, one 

 on either side of the median crest. He pointed out that most 

 probably the coarsely fibrous structure of the crest on the dorsal 

 surface of the spine proved the attachment of muscular tissue, 

 " which connected it with and served to elevate the spine above." 

 On a male specimen of the living Chimcera (PI. XII, Fig. 8) I have 

 observed that the highest tendons of the superficial portion of 

 the adductor mandibularis (Levator anguli oris — term)^ are attached 

 not only on the anterior surface of the free, upwardly-curved, 

 proxiiBal portion of the spine-like process, but also that the fibres 

 of its deeper portion are connected with the whole ventral surface 

 so far as there is space for their insertion. A branch of the tendon 

 is attached also to the under surface of the skin covering the spine. 

 These muscles tend to depress the spine, but there is none to elevate 

 it. The round free process, quite separate from the cranium, is held 

 in place by two dorsal tendon-like ligaments instead of muscles, and 

 these reach from the dorsal surface of the proximal expansion of the 

 spine to the prominent supra-orbital roof of the cranium (PI. XII, 

 Fig. 8). These tendons and the bundles of muscular fibres on the 

 other side in Squaloraja could only have served to fix the spine when 

 pressed in attack, which explains why free tubercles of the integu- 

 ment are confined to the lateral and dorsal side of the proximal 

 portion of the spine. 



As regards the internal structure of the frontal spine, we must 

 remark first that it is hollow (PI. XII, Fig. 5), but becomes more 

 and more compact proximally. As in Chimcera (PL XII, Fig. 12), 

 the dorsal wall of the cavity is much thinner than the ventral wall. 

 In transverse section (Fig. 5) we may observe with a lens a number 

 of capillary canals in the thick calcified wall ; and two smaller main 

 canals can be seen perforating the whole length of the spine, one on 

 either side. 



The microscopical structure of the spine is quite the same as in 

 Ischyodus and Chimcera. A number of vascular canals are to be 

 seen, and between these there are large cells. The elongated form 

 of the cells is observed especially in the longitudinal section, and 

 they differ usually from the cells in the prismatic granules of the 

 calcified hyaline cartilage of the internal skeleton of Elasmobranchs, 

 especially from those of the Holocephala. They are irregularly 

 arranged, and the intercellular tissue is fibrous, but this never 

 1 B. Vetter, Jena Zeitschr. f. Naturw., vol. xii, p. 441. 



