224 Mammalia, 



fibres are arranged at right angles to those of the Digastric, 

 being very careful not to cut away the nerve that lies 

 between these two muscles, whose apparent posterior ex- 

 tremity, i.e., as far as at present traceable, is internal to the 

 ramus of the jaw where it was cut across (and which may be 

 therefore sometimes destroyed in the fracture). 



The muscle immediately underlying the anterior belly of 

 the Digastric is the Mylo-hyoid* ; it forms with its fellow of 

 the opposite side a muscular floor for the cavity of the mouth ; 

 and arises from the whole length of the internal superior 

 margin of the body of the jaw (the mylo-hyoid ridge), from 

 the symphysis to the last molar tooth. The posterior fibres 

 pass obliquely backwards, and may be traced, internal to the 

 Digastric, to be inserted into the body of the os-hyoides ; the 

 middle and anterior fibres (as will be later shown) are inserted 

 into a median fibrous raphe, where they join at an angle 

 with the fibres of the opposite muscle. This Mylo-hyoid is 

 distinctly double ; the anterior bundle having an extended 

 longitudinal development, while the posterior division is 

 short, and has its fibres directed transversely outwards. 



The nerve exposed, running the whole length of the Mylo- 

 hyoid muscle, is the Mylo-hyoid nerve, a branch derived 

 from the Inferior Dental Nerve, just as that nerve is about 

 to enter the dental foramen. It descended in a groove on the 

 inner surface of the ramus of the jaw, in which it was re- 

 tained by a process of fibrous membrane. It supplies the 

 cutaneous surface of the Mylo-hyoid muscle, and the anterior 

 belly of the Digastric. 



Dissection of Chorda Tympani, Gustatory Nerve, 

 Whartonian Duct, and Submaxillary Plexus. The 



* ixv\r)y a mill, the jaw ; and v (the letter upsilon) tlZos, shape, the thence- 

 named Hyoid bone. 



