904 



PARTURITION. 



the posterior auricular, the digastric, and the 

 stylo-hyoid. 



The posterior auricular nerve passes off from 

 the anterior part of the portio dura ; it passes 

 upwards and forwards round the anterior sur- 

 face of the mastoid process, and is joined by 

 the great auricular nerve of the cervical plexus; 

 it then becomes superficial, accompanies the 

 artery of the same name, and is distributed to 

 the ear and side of the head. 



The digastric nerve passes backwards and is 

 distributed by several filaments to the posterior 

 belly of the digastric muscle. It sends ananasto- 

 motic filament to the glosso-pharynaeal nerve. 



The sti/lo-hyoid nerve arises often from a 

 common trunk with the preceding; it enters the 

 stylo-hyoid muscle after passing along its supe- 

 rior border. 



After the portio dura has given off the above- 

 mentioned branches it passes forwards through 

 the substance of the parotid gland below the 

 ineatus auditoriusexternus; it then crosses over 

 the posterior auricular artery and the styloid 

 process, the external jugular vein and the ex- 

 ternal carotid artery, and before reaching the 

 ramus of the jaw it divides into two branches, 

 the tempero-facial and the cervico-facial, which 

 diverge from each other. 



The tempero-facial division passes upwards 

 and forwards in the substance of the parotid, 

 forming with the trunk of the facial nerve an 

 arch, the concavity of which is above; it then 

 crosses the neck of the lower jaw and receives 

 at this point one and sometimes two branches 

 from the auriculo-temporal branch of the in- 

 ferior maxillary nerve. The tempero-facial 

 nerve then breaks up into a number of branches 

 which anastomose and form arches, from the 

 convexities of which proceed a number of di- 

 verging filaments, some of which pass upwards 

 and others forwards, emerging from beneath 

 the parotid, to be distributed to the muscles of 

 the face. 



The cervico-facial division is smaller than 

 the preceding ; it takes the same direction as 

 the trunk of the nerve, passing downwards 

 and forwards in the substance of the parotid ; 

 at the angle of the jaw it divides into three or 

 four branches ; these subdivide into secondary 

 branches, some of which pass forwards to sup- 

 ply the muscles of the lower part of the face, 

 while others are distributed to the upper part 

 of the cervical region. 



Lymphatic glands. Several lymphatic glands 

 are 'found imbedded in the superficial surface, 

 and in the substance of the parotid. These 

 may readily be distinguished from the tissue 

 of the parotid by their red colour. They 

 are not uncommonly the seat of disease, and 

 if their removal becomes necessary the opera- 

 tion may be done without much difficulty and 

 without great risk of wounding any important 

 textures. But a slight consideration of the 

 deep connexions of the parotid and of its close 

 relations to the many important parts which 

 pass through it, and by which it is surrounded, 

 will be sufficient to convince the surgeon that 

 the removal of this gland cannot be effected 

 without extreme difficulty and danger, and 



that it must necessarily be attended by injury 

 to some of the important parts in this region. 

 The division of the facial nerve, and conse- 

 quent palsy of the face, may be looked upon 

 as one of the most serious and certain conse- 

 quences of an attempt to excise the parotid. 



(George Johnson.) 



PARTURITION, MECHANISM OF. 



Parturition is the act in which the matured fruit 

 of healthy conception and gestation is transmit- 

 ted along the passages of the mother. " Rien 

 de plus curieux que le mechanisme par lequel le 

 foetus est expulse ; tout s'y passe avec une pre- 

 cision admirable," is the quotation which the 

 celebrated Naegele has used for a heading to his 

 essay on this important process in the human 

 subject, the first in which it has been completely 

 and accurately described. Perhaps in no de- 

 partment of physiology do we gain so mucli 

 instruction from comparative anatomy as here ; 

 when we examine the ovipara, especially the 

 higher orders of them, we are struck with the 

 simplicity of the parturient process, and with 

 the equally simple laws by which it is governed. 

 The oval form of the egg shows that its long dia- 

 meter must run parallel with the canal through 

 which it lias to pass, and in these classes of 

 animals this single law constitutes nearly the 

 whole mechanism of parturition in them. 



In the vivipara the process becomes some- 

 what more complicated ; the foetus enveloped 

 in its soft and fluctuating bag of membranes 

 and the more perfect pelvis bring many other 

 relations into play which do not exist in the 

 lower classes ; hence in the viviparous animals 

 we see that the manner in which the foetus ad- 

 vances through the passages of the mother 

 varies considerably, still however not so much 

 as to render it incompatible with the law above 

 mentioned. 



In considering the process of parturition in 

 the lower classes of animals it will be scarcely 

 necessary to go beyond the Vertebrata, for in 

 the lowest classes, especially the zoophytes, it 

 admits of but little comparison with them, the 

 analogy rather inclining in the contrary direc- 

 tion, viz. towards the vegetable kingdom. In 

 some of the other classes, viz. Vermes, &c., 

 little certain is known as to this process beyond 

 that the generative organs are of the simple 

 tubular character; we must except, however, 

 the Insecta, in many of which the ova and the 

 mode of their expulsion strongly resemble a 

 much higher class, viz. the Aves. 



The Fishes, which are the lowest class of the 

 Vertebrata, have no bony canal or pelvis ; the 

 whole apparatus for parturition is a tube the 

 lower part of which at least is fibrous ; in the 

 larger fishes it is muscular and capable of con- 

 siderable dilatation. In the Ray and Shark 

 tribe we first see this canal divided into two 

 parts, viz. the ovary and oviduct; still the pro- 

 cess is of the simplest character, the ova being 

 propelled precisely like the contents of an in- 

 testinal tube In the viviparous sharks, the Blen- 

 nius viviparus, and still more remarkably in 

 the Cetacea, where as belonging to the Mam- 

 malia we first see the oviduct divided into a 



