32 



Mr. G. E. Dobson. 



[Mar. 31, 



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 jaw at a short distance in front of their origin. 

 Here then we have a vertical tendinous intersection unconnected with 

 the hyoid bone. The mylo-hyoids are altogether absent, their places 

 and part of their function being evidently taken by the united 

 digastrics, which extend almost the whole length of the jaws ; while 

 their action on the hyoid is performed by the greatly developed genio- 

 hyoid muscles. 



In the much larger but externally very similar species,* Epomo- 

 phorns franqueti, the anterior bellies of the digastrics are single and 

 not united between the rami of the mandible, and the mylo-hyoids 

 are present and well developed ; the tendinous intersection described 

 above is, nevertheless, visible, and though much less defined than in 

 E. minor, occupies precisely the same relative position, and has the 

 same vertical direction. 



In Herpestes nipalensis the digastrics are very large and united 

 between the jaws ; the tendinous intersection is nearly vertical and is 

 continued inwards to unite with the corresponding band from the 

 opposite side slightly behind the hyoid bone. The raphe thus formed 

 is connected with the fascia covering the sterno-hyoid muscles ; and 

 the deep surface of the united bellies is inseparably united, along the 

 middle line, with the very feebly developed mylo-hyoids which they 

 conceal altogether. 



In man, as an anomaly, the fibres of the two anterior bellies have 

 been found blended with each other, and expanded into a muscular 

 plane with considerable attachment to the jaws ;t or the anterior 

 belly has been found double, the second part uniting with its fellow 

 in a median raphe below the chin, overlapping the mylo-hyoid 

 muscle ;J or the tendon of intersection not unfrequently is continued 

 from one side across to the other, forming a zone immediately above 

 the hyoid bone, to the body of which it is tied down by fibrous tissue ; 

 from the upper surface of this the anterior bellies arise, either a, 

 distinct, or f3, more rarely inseparable. § 



It may be observed that this last described condition is precisely 

 that of the same muscles in Tupaia ellioti, and is extremely interest- 

 ing, as evidently indicating reversion to a state of the muscle, pro- 

 bably once normal in ancient mammalian types, and which is now 

 represented in man and most other mammals by a fascial layer only — 

 the supra-liyoid aponeurosis — which, springing from the tendons of the 



* All the species of this genus agree very closely in certain external characters. 

 (See " Catal. Chiropt. Brit. Mus.," p. 5.) 

 f Fleischmann, quoted by McWhinnie, " Lond. Med. G-az.," xxxyii, p. 186. 

 X Wood, quoted by Macalister, " Trans. Roy. Irish Acad.," xxy, p. 33. 

 § Macalister, loc. cit. 



