30 



Mr. G. E. Dobson. 



[Mar. 31, 



tendon, or having their limits defined by an intermediate tendinous 

 intersection. In most mammals, however, this tendinous intersection 

 is either very feebly defined, or it is altogether absent. What, then, 

 is its meaning when present, and on what does its relative development 

 depend ? 



The distinct tendon which exists between the anterior and posterior 

 bellies of the digastric in man and in other Primates, might reasonably 

 be supposed to be produced by tension from the aponeurotic loop, which 

 attaches it to the greater cornu of the hyoid bone ; but in many species 

 of other orders a tendon or tendinous intersection is found where the 

 connexion of this muscle with the hyoid bone is either very feeble, or 

 distributed equally over the whole extent of its anterior belly, or 

 obsolete ; and in which, moreover, the direction of the intersection, 

 where it traverses the substance of the muscle, is almost invariably 

 oblique* and directed downwards, forwards, and inwards in a direction 

 leading from and not towards the hyoid. The true significance of the 

 tendinous intersection is to be found, as I shall endeavour to show, in 

 the remarkable form assumed by the anterior belly of the muscle in 

 certain species. 



While engaged in the dissection of a specimen of that rare mammal 

 Gymnura rafflesii,f I was much strnck by the peculiar form of the 

 anterior belly of the digastric. About the middle of the muscle, at its 

 narrowest part, it is traversed by an oblique tendinous intersection 

 more marked internally, arising from the upper margin, which is con- 

 tinued inwards and slightly forwards from its lower and internal 

 margin as a tendinous band across the mylo-hyoid muscle, to unite in 

 front of the hyoid bone with the corresponding band from the opposite 

 side. From the tendinous raphe thus formed, muscular fibres arise, 

 which, extending forwards and inwards, cover -the anterior three- 

 fourths of the mylo-hyoid and part of the genio-hyoid muscles, and 

 passing above the margins of the anterior bellies of the digastric 

 muscles of opposite sides, are inserted with them and for some distance 

 in front of them, into the rami of the mandible. 



This horizontal muscular expansion, w T hich takes its origin thus 

 from the tendinous intersection and its median continuation, might 

 also be described as a deep division of the anterior belly of the muscle, 

 commencing at the tendinous intersection, and uniting with its fellow 

 of the opposite side along the middle line between the jaws. Its 



* In some species it is nearly straight, but this does not depend on attachment to 

 the greater cornu of the hyoid bone, as I purpose showing further on. 



f I owe the opportunity which has been afforded me of examining the anatomy 

 of this rare species to tbe kindness of Mr. W. T. Blanford, F.R.S., whom I have 

 also to thank for many specimens of Oriental Insectivora, which have furnished me 

 with much valuable material in working out my systematic and anatomical mono- 

 graph of the Insectivora. 



