MR. G. E. DOBSON ON THE DIGASTRIC MUSCLE. 261 



in front, and the mylo-hyoid muscles are well developed ; nevertheless, the presence of a 

 nearly vertically transverse tendinous inscription across the digastrics of those last- 

 named species, corresponding precisely iu position and direction to the origin of the 

 tendinous raphe bounding the united anterior bellies of the muscles behind in the first 

 named, indicates a united state of the digastrics in a common ancestor. It is espe- 

 cially interesting to note that in these species, where union of the muscles extends so far 

 backwards, the tendinous intersection is vertical or nearly so, and the direction of the 

 fibres of the deep or internal lamina transverse, while those of the superficial external 

 part spring from it at right angles to its direction and pass forwards to their insertion 

 into the mandible. Here, then, we have a vertical tendinous intersection unconnected 

 with the hyoid bone ! 



In the genus Erinacetis, which with Gymnura makes up the family Erinaceidae, 

 although the digastrics are no longer united, a superficial oblique tendinous inscription 

 occupies precisely the same position as in Gymnura, though much less developed ; it 

 extends from the upper margin of the muscle (which is nearly of the same calibre 

 throughout), and on reaching its lower margin is continued inwards into a fascial 

 expansion extending between the anterior bellies of the muscles of opposite sides, 

 covering the mylo-hyoid muscle, but no muscular fibres arise from it as in Gymnura; 

 nevertheless this fascial expansion evidently represents the muscular sheath of the 

 expanded and united digastrics iu the ancestral forms. 



In Centetes ecaudatus and semispinosus, in Pteropus eclulis and medius, and probably 

 in all the species of that genus, in Epomophorus franquetl, comptus, and pusillus, in 

 Megaderma lyra, in Cavia apercea, in JPkoca communis, and in other species, though the 

 fascial expansion be absent or feebly marked, the transverse tendinous inscription is 

 traceable, although its presence in some, as in Centetes ecaudatus, is indicated by a faint 

 superficial oblique line surrounding the muscle. 



In Tupaia ellioti the anterior bellies of the digastrics also unite in the middle line 

 between the jaws; but there is no separate superficial external lamina in direct con- 

 tinuation with the posterior belly, as in Gymnura rafflesih. The intersecting tendon is 

 narrower but more distinct, arises, as in that species, from the upper margin of the 

 muscle, and is continued downwards, forwards, and inwards to unite with the correspond- 

 ing tendon from the opposite side across the mylo-hyoid, precisely as in Gymnura 

 rafflesu ; but unlike its free condition in that species it is closely adherent by its deep 

 surface to the mylo-hyoid muscle, and connected with the hyoid bone by a strong fibrous 

 aponeurosis. The united anterior bellies pass forwards, taking their origin from the 

 tendinous raphe, and, separating slightly near the symphysis menti, are inserted into the 

 rami of the mandible, and by a fibrous aponeurosis into the symphysial angle. The 

 mylo-hyoid muscles, nearly wholly concealed by them, are feebly developed. 



In If us decumanus and in other species of the genus the digastrics are united in front, 

 the posterior margin of the united muscles being formed by the united intermediate 

 tendons which are connected with the hyoid bone ; in Myoxus avellanarius the inter- 

 mediate tendons are even better developed, and the united anterior bellies are closely 

 connected with the mylo-hyoid muscles. In Cercopithecus callitrichus, in Troglodytes 



