138 DISSECTION OF THE HEAD. 



The OLFACTORY NERVE (fig. 33, l ) forms a bulb on the cribriform plate 

 of the ethmoid bone, and sends branches to the olfactory region of the 

 nose through the apertures in the roof. These branches are about twenty 

 in number, and are divisible into three sets. An inner set, the largest, 

 descend in the grooves on the septum nasi, and branching, extend over 

 the upper third. A middle set is confined to the roof of the nose. And 

 an external set is distributed on the upper spongy bone, on the anterior 

 square surface of the os ethmoides, and on the fore part of the middle 

 spongy bone. 



As the branches of the olfactory nerve leave the skull, they receive 

 tubes from the dura mater and pia mater, which are lost in the tissue to 

 which the nerves are distributed. The nerves ramify in the pituitary 

 membrane in tufts of filaments which communicate freely with the con- 

 tiguous twigs, forming a network, but their mode of termination in the 

 tissue is unknown. It has been suggested by Schulze that they join the 

 deep processes or ends of the so-called olfactorial cells ; but this union has 

 not been seen. 



The olfactory nerve differs in structure from the other cranial nerves ; 

 for its branches are deficient in the white substance of Schwann, are not 

 divisible into fibrilke, and are nucleated and granular in texture. They 

 resemble the ganglionic fibres : and seera to consist of an extension of the 

 nerve substance of the olfactory bulb. 



The other nerves in the nose will be described in the following section. 



Bloodvessels. For a statement of the different vessels of the nose, see p. 

 141. The arteries form a network in the pituitary membrane, and a 

 large submucous plexus on the edge of each of the two lower spongy bones, 

 especially on the inferior. The veins have a plexiform disposition like 

 the arteries, and this is largest on the lower spongy bone and the septum 

 nasi. 



SECTION XIV. 



SPHENO-PALATINE AND OTIC GANGLIA, FACIAL AND NASAL NERVES, 

 AND BRANCHES OF THE INTERNAL MAXILLARY ARTERY. 



THE preparation of Meckel's ganglion and its branches (fig. 34), and of 

 the terminal branches of the internal maxillary artery, is a somewhat diffi- 

 cult task in consequence of the nerves and vessels being contained in 

 osseous canals which require to be opened. As is the case with other 

 dissections, the student seeks first the branches, and traces these to the 

 ganglion and main trunk. 



Dissection. The left half of the head is to be used for the display of the 

 ganglion and its branches; but the student may previously acquire some 

 skill by attempting the dissection on the remains of the right side. 



To lay bare the branches of the palate, detach the soft parts in the roof 

 of the mouth from the bone, until the nerves and vessels escaping from the 

 posterior palatine foramina are arrived at. Cut off, with a bone forceps, 

 the posterior part of the hard palate to a level with the vessels and nerves ; 

 and cleaning these, trace offsets behind into the soft palate, and follow the 

 main pieces forwards to the front of the mouth. 



Take away without injury to the naso-palatine nerve and vessels (already 



