24 DISSECTION OF THE HEAD. 



put into numerous large offsets ; these spread over the posterior part of 

 the occipito-frontalis muscle, ending mostly in the integument. As soon 

 as the nerve pierces the trapezius, it is joined by an offset from the third 

 cervical nerve ; and on the back of the head it communicates with the 

 small occipital nerve. 



The small occipital nerve of the cervical plexus (fig. 2, 2 ) lies midway 

 between the ear and the preceding nerve, and is continued upwards in the 

 integuments higher than the level of the ear. It communicates with the 

 nerve on each side, viz., the posterior auricular and the great occipital. 

 Usually this nerve furnishes an auricular branch to the upper part of the 

 ear at the cranial aspect, which supplies also the attollens aurem muscle. 



SECTION II. 



INTERNAL PARTS OF THE HEAD. 



Dissection. The skull is now to be opened, but before sawing the bone 

 the dissector should detach, on the right side, the temporal muscle nearly 

 down to the zygoma, without separating the fascia of the same name from 

 the fleshy fibres ; and all the remaining soft parts are to be divided by an 

 incision carried around the skull, about one inch above the margin of the 

 orbit at the forehead, and as low as the protuberance of the occiput. 



The cranium is to be sawn in the same line as the incision through the 

 soft parts, but the saw is to cut only through the outer osseous plate. The 

 inner plate is to be broken through with a chisel, in order that the subja- 

 cent membrane of the brain (dura mater) may not be injured. The skull- 

 cap is next to be forcibly detached by inserting the fingers between the 

 cut surfaces in front, and the dura mater will then come into view. 



The DURA MATER is the most external of the membranes investing the 

 brain. It is a strong, fibrous structure, which serves as an endosteum to 

 the bones, and supports the cerebral mass. Its outer surface is rough, 

 and presents, now the bone is separated from it, numerous small fibrous 

 and vascular processes ; but these are most marked along the line of the 

 sutures, where the attachment of the dura mater to the bone is the most 

 intimate. Ramifying on the upper part of the membrane are branches of 

 the large meningeal vessels. 



Small granular bodies, glands of Pacchioni, are also seen along the 

 middle line. The number of these bodies is very variable ; they are found 

 but seldom before the third year, but generally after the seventh, and 

 they increase with age. Occasionally the surface of the skull is indented 

 by these so-called glands. 



Dissection. For the purpose of seeing the interior of the dura mater, 

 divide this membrane with a scissors close to the margin of the skull, 

 except in the middle line before and behind where the superior longitudi- 

 nal sinus lies. The cut membrane is then to be raised towards the top of 

 the head ; and on the right side the veins connecting it with the brain 

 may be broken through. 



The inner surface of the dura mater is smooth and polished ; and this 

 appearance is due to an epithelial layer similar to that lining serous 

 membranes. 



