Drxon— On the Development of the Branches of the Fifth Cranial Nerve in Man. 61 
Empryo F.M.—(7 weeks, 17°5 mm.). Figures 9 & 10, Plate I. 
The inferior maxillary nerve rises from the lower part of the Gasserian 
ganglion, just in front of its lower end. The nerve passes downwards and 
forwards to the upper border of Meckel’s cartilage, where it breaks up into its 
branches. The length of this part of the nerve is only 0-4 mm., and from it the 
nerve to the internal pterygoid muscle passes inwards. 
The inferior dental nerve, as regards direction, is the continuation of the main 
trunk of the inferior maxillary. From its origin, at the upper border of Meckel’s 
cartilage, the inferior dental nerve passes downwards and forwards, lying on 
Meckel’s cartilage, close to its upper edge. The nerve is at first close to the cartilage, 
but as it passes inwards, it comes to lie some distance in front, and to the outer 
side of, the cartilage. In section, the ossifying mandible is seen to form a crescent 
of bone (figs. 19 and 20, Plate II.), in front and to the outer side of the nerve, so 
that the nerve is found to lie between Meckel’s cartilage and the bone of the 
developing lower jaw. ‘This bony plate, as it is traced in towards the middle 
line, divides into an upper and a lower segment. Through the gap left between 
these two parts of the bone the greater part of the inferior dental nerve escapes 
as the mental branch. The mental nerve at once divides into numerous twigs, 
which come towards the surface. Before the inferior dental passes through the 
bone it gives off at least two fine twigs, which pass up inside the bony plate to 
the ‘‘ Zahnleiste.” Further a very fine twig is carried on towards middle line, 
inside the bony plate, after the rest of the nerve has passed out. ‘The length of 
the inferior dental is 1-6 mm. 
The mylo-hyoid branch rises from the inferior dental close to the origin of the 
latter, and passing more downwards than the inferior dental, it crosses the outer 
surface of Meckel’s cartilage, obliquely, from above, downwards, and forwards. 
Having reached the lower border of Meckel’s cartilage, it is continued along it, 
towards the middle line. Before the nerve ends it lies a good deal lower than the 
cartilage. Its fibres end in the superficial part of the mylo-hyoid muscle. The 
length of the mylo-hyoid nerve is 1°6 mm. 
The auriculo-temporal nerve, takes origin from the superficial surface, of the 
inferior maxillary division of the fifth nerve, and first turns directly outwards. 
The nerve soon turns downwards, crossing the meningeal artery, and then passes 
almost vertically downwards, over the outer aspect of Meckel’s cartilage. The 
auriculo-temporal nerve crosses the cartilage nearer to its outer and upper end 
than the mylo-hyoid nerve does. The nerve, having crossed the cartilage, lies in 
front of the external auditory pit, where it breaks up into branches, which, 
turning towards the surface, come into relation with branches of the facial nerve. 
K 2 
