DURA MATER. 50T 



THE BRAIN AND ITS MEMBRANES. 



Dissection. To examine the brain with its membranes, the skull-cap should first be removed. 

 This may be effected by sawing through the external table, commencing, in front, about an inch 

 above the margin of the orbit, and extending, behind, to a level with the occipital protuberance. 

 The internal table must then be broken through with the chisel and hammer, to prevent injury 

 to the investing membranes or brain, and, after having been loosened, it should be forcibly detached, 

 when the dura mater will be exposed. The adhesion between the bone and the dura mater is 

 very intimate, and much more so in the young subject than in the adult. 



The membranes of the brain are, the dura mater, arachnoid membrane, and pi a 

 mater. 



DURA MATER. 



The dura mater is a thick and dense inelastic fibrous membrane, which lines 

 the interior of the skull. Its outer surface is rough and fibrillated, and adheres 

 closely to the inner surface of the bones, forming their internal periosteum, this 

 adhesion being more intimate opposite the sutures and at the base of the skull ; 

 at the margin of the foramen magnum it becomes continuous with the dura 

 mater lining the spinal canal. Its inner surface is smooth and epitheliated, 

 being lined by the parietal layer of the arachnoid. The dura mater is, therefore, 

 a fibro-serous membrane, composed of an external fibrous lamella, and an internal 

 serous layer. It sends numerous processes inwards, into the cavity of the skull, 

 for the support and protection of the different parts of the brain ; it is also pro- 

 longed to the outer surface of the skull, through the various foramina which 

 exist at its base, where it is continuous with the pericranium; and its fibrous layer 

 forms sheaths for the nerves which pass through these apertures. At the base 

 of the skull, it sends a fibrous prolongation into the foramen crecum ; it lines the 

 olfactory groove, and sends a series of tubular prolongations round the filament; 

 of the olfactory nerves as they pass through the cribriform foramina ; a prolonga- 

 tion is also continued through the sphenoidal fissure into the orbit, and another 

 is continued into the same cavity through the optic foramen, forming a sheath for 

 the optic nerve, which is continued as far as the eyeball. In certain situations in 

 the skull already mentioned, the fibrous layers of this membrane subdivide, to 

 form sinuses for the passage of venous blood. Upon the upper surface of the 

 dura mater, in the situation of the longitudinal sinus, may be seen numerous 

 small whitish bodies, the glandule Pacchioni. 



Structure. The dura mater consists of white fibrous and elastic tissues, arranged 

 in flattened laminae, which intersect one another in every direction. , 



Its arteries are very numerous, but are chiefly distributed to the bones. Those 

 found in the anterior fossa are the anterior rneningeal, from the anterior and 

 posterior ethmoidal, and internal carotid. In the middle fossa are the middle and 

 small meningeal, from the internal maxillary, and a third branch from the 

 ascending pharyngeal, which enters the skull through the foramen lacerum basis 

 cranii. In the posterior fossa, are the posterior meningeal branch of the occipital, 

 which enters the skull through the jugular foramen; the posterior meningeal, from 

 the vertebral ; and occasionally meningeal branches from the ascending pharyn- 

 geal, which enter the skull, one at the jugular foramen, the other at the anterior 

 condyloid foramen. 



The veins, which return the blood from the dura mater, and partly from the 

 bones, anastomose with the diploic veins. These vessels terminate in the various 

 sinuses, with the exception of two which accompany the middle meningeal artery; 

 these pass from the skull at the foramen spinosum. 



The nerves of the dura mater are, the recurrent branch of the fourth, and fila- 

 ments from the Casserian ganglion, the ophthalmic nerve, and sympathetic. 



The so-called glandulae Pacchioni are numerous small whitish granulations, 

 usually collected into clusters of variable size, which are found in the following- 

 situations : 1. Upon the outer surface of the dura mater, in the vicinity of the. 



