GUIDE TO THE HEAD AND NECK 1589 



shown: (i) the geniculate ganglion, giving off {a) the great superficial petrosal 

 nerve, (b) a communicating branch to the small superficial petrosal nerve, and 

 (c) the external superficial petrosal nerve (inconstant), all these being situated 

 in the first portion of the aqueduct ; and (2) the following branches, arising in 

 the third part of the aqueduct, namely, (a) the nerve to the stapedius muscle, 

 (b) the chorda tympani nerve, and (c) a communicating branch to the auri- 

 cular branch (Arnold's nerve) of the pneumogastric. 



Articulations of the Atlas, Axis, and Occipital Bone. — The ligaments of these 

 joints are to be dissected according to the descriptions given of them in the 

 text, and the movements allowed between the occipital bone and the atlas, 

 and between the atlas and axis, are to be carefully studied. In particular, 

 the following ligaments require special attention : (i) the transverse ligament 

 of the atlas, with the extensive synovial membrane between it and the odontcid 

 process of the axis ; (another synovial membrane is to be noted between the 

 odontoid process and the anterior axch of the atlas) ; (2) the cruciform ligament, 

 of which the preceding forms a part; (3) the lateral odontoid or alar liga- 

 ments ; and (4) the posterior occipito-axial ligament, or membrana tectoria, 

 which covers the other ligaments just enumerated. 



Certain of the ligaments under consideration admit of being dissected from 

 the exterior. These are as follows : (i) the atlanto-axial — anterior, postei ior, 

 and capsular ; and (2) the atlanto-occipital — anterior, posterior, and cap- 

 sular. The others, however, are situated within the spinal canal, in relation 

 to its anterior wall. These are as follows : (i) the posterior occipito-axial, 

 or membrana tectoria ; (2) the accessory atlanto-axial ligaments ; (3) the 

 cruciform ligament, of which the transverse ligament of the atlas constitutes 

 a part ; (4) the lateral odontoid or alar ligaments ; and (5) the middle odontoid, 

 or suspensory, ligament. In order to display the ligaments which are situatetl 

 within the spinal canal, the posterior arch of the atlas and the neural arch of the 

 axis should be cut through with the saw. The tabular part of the occipital 

 bone is to be sawn across a little behind the occipital condyles, and the pos- 

 terior arch of the atlas and the neural arch of the axis are also to be sawn 

 through. After removal of the dura mater, the first ligament to be dissected 

 is the posterior occipito-axial, or membrana tectoria, which, as stated, co%eis 

 the others, and should be detached from the axis and turned upwards after it 

 has been examined. The cruciform ligament having been studied, the final 

 stage in this intricate dissection consists in detaching the superior crus of the 

 vertical part of the cruciform ligament from the basilar groove of the occipital 

 bone, and turning it carefully downwards. 



The Eyeball. — The dissection of the human eyeball can only be accom- 

 plished on perfectly fresh specimens. In order to prepare himself for this the 

 dissector is recommended to obtain several eyeballs of the ox, say five or six. 

 The fat, ocular muscles, conjunctiva, and capsule of Tenon are to be removed 

 by dividing, with the scissors, the capsule of Tenon and the conjunctiva in a 

 circular manner at the comeo-scleral junction. The adjuncts of the sclerotic 

 can then be stripped off in a backward direction towards the optic nerve. 

 In detaching the capsule of Tenon from the sclerotic the perisclerotic lymph- 

 space, or Tenon's space, is to be noted. The venae vorticosae will probably 

 also be seen. These are usually four in number, and they pierce the sclerotic 

 about midway between the optic entrance and the comeo-scleral junction, 

 at points equally distant from each other. Near the comeo-scleral junction 

 the anterior ciliary arteries may be seen piercing the sclerotic, and around the 

 entrance of the optic nerve the ciliary nerves and posterior ciliary arteries may 

 be seen piercing the sclerotic. 



It is well that the eyeballs should be prepared for dissection by keeping 

 them in a 10 per cent, solution of formalin, which may sufficiently harden 

 them. There being several ox's eyeballs at the disposal of the dissector, it 

 will be to his advantage to make use of two of them in the following 

 manner: (i) divide one eyeball into two halves, inner or nasal, and outer or 

 temporal, by making an antero-posterior cut along the sagittal axis, or axis 

 of vision — that is to say, a line connecting the anterior and posterior poles of 

 the eyeball ; and (2) divide another eyeball into two halves, anterior and 

 posterior, by making a cut along the course of the equator. These two sections 



