ANATOMY. 



to the passions of the mind, and thereby 

 distend the lig-amentous tubes until they 

 feel perfectly hard and rigid, in which 

 state the whole organ is fitted for the 

 function which it has to perform in the 

 act of copulation. The urethra, sur- 

 rounded by its spongy substance, runs 

 along the under surface of the corpora 

 cavernosa, and the glans penis is situated 

 at the anterior extremity of these parts. 



The body of the penis is covered by 

 c-ommon integuments, which, being adapt- 

 ed to cover the organ in its extended 

 state, fall into wrinkles when it is col- 

 lapsed. These are continued beyond the 

 end of the glands, and are inflected, so as 

 to form a hood or covering to the glans, 

 called the prepuce. The latter part is 

 connected to the mouth of the urethra by 

 a snnill fold named the frenum. The 

 surface of the glans, and the lining of 

 the prepuce, are smeared with an unctu- 

 ous matter of peculiar odour, furnished 

 by some small glands. 



OF THE BRAIX AX1) NERVES. 



The brain is a soft and somewhat white 

 substance, situated in the cavity of the 

 skull, and corresponding in form to that 

 cavity. Its parts are supported by a firm 

 membrane, called the dura mater, and its 

 substance is more immediately invested 

 by a delicate membrane, called the pia 

 mater. 



The structure of the brain is remark- 

 ably constant and uniform ; very seldom 

 deviating from the accustomed standard. 

 Varieties of formation occur, not unfre- 

 quently, in most other parts of the body ; 

 but the parts of the brain preserve an al- 

 most invariable relation of form, position, 

 magnitude, and connection; which seems 

 to prove, that the right performance of 

 the functions of this organ requires an 

 exactness in the structure of individual 

 parts. 



According to Soemmerring, the weight 

 of the brain varies from "2lb. 5oz. to 3/A. 

 3|or. Of two hundred brains, which this 

 anatomist examined, none weighed four 

 pounds, whereas Haller states its weight 

 as amounting in general to five pounds. 

 The weight of the brain, compared to 

 that of the body, is an inverse ratio to 

 the age of the subject In young foetuses 

 it is soft and almost fluid : it becomes of 

 a more solid consistence in increasing 

 age, and is firmest in old persons. 



The dura mater is a very firm and 

 compact membrane, adhering closely by 

 vessels and fibres to the internal surface 



VOL I 



of the cranium. It is therefore to be re- 

 garded as the periosteum of the i 

 table of the cranium, as well as u innii- 

 brane for supporting and investing t he- 

 brain. It is described by anatonn 

 consisting of two layers, intimately con- 

 nected in general, but separated from 

 each other at particular parts, so as to 

 leave vacancies between th:.-in, called si- 

 nuses, into which the veins of the brain 

 pour their blood. The chief of these ure, 

 the superior longitudinal, the two lateral, 

 and the torcular herophili. There are 

 besides some smaller ones, as the infe- 

 rior longitudinal, the cavernous, the cir- 

 cular, the superior, and the anterior pe- 

 trosal. They all terminate ultimatelv in 

 the lateral sinus, which, quitting the cra- 

 nium, takes the name of internal jugular 

 vein. 



On the upper part of the dura mater 

 some small eminences are observed, aris- 

 ing from clusters of white granular bo- 

 dies, situated between this membrane 

 and the pia mater; they are the glandulac 

 Pacchioni, and fill the pits which may be 

 observed in the skull-cap. The ramifica- 

 tions of the'spinous artery, which is the 

 cliief nutrient vessel of the dura mater, 

 are very conspicuous on each side of the 

 head. The inner surface of the dura 

 mater is smooth and shining, and has no 

 connection with the pia mater, except 

 where veins pass from the latter mem- 

 brane to the sinuses. 



The processes which the dura mater 

 forms, for separating and supporting the 

 different parts of the brain, are, 1. the 

 falx cerebri ; 2. tentorium cerebelli ; 3. 

 falx cerebelli. 



The two membranes which immedi- 

 ately invest the brain were considered as 

 one, and called the pia mater, until a 

 more minute investigation had shewn 

 that it could be divided into two layers. 

 The outer one is called tunica arachnoi- 

 dea. This is spread over the visible sur- 

 face of the brain, is of a pale white co- 

 lour, yet in in some degree transparent, 

 very thin, and devoid of evident vessels. 

 It is seen most evidently, where it passes 

 betweenthe two lobes of the cerebellum, 

 and about the middle of the basis cere- 

 bri : in other parts it adheres so inti- 

 mately to the pia mater, that the distinc- 

 tion can scarcely be demonstrated. 



The pia mater every where covers the 

 external surface of the brain, and there- 

 fore sends processes into all the convolu- 

 t tins organ. It is extreiiu K \.i^. 

 cular, and a great portion of the blood, 

 which the brain receives, is spread out 



Ud 



