494 DEPOSITS IK THE MEMBRANES OF THE BRAIN. 



tumours are more or less globular, nodulated, with a dis- 

 tinct pedicle, and convoluted. The eminences or apparent 

 convolutions are due to the manner in which the dura mater 

 binds down the growth as it developes, and is fixed in 

 depressions which are not unlike the furrows of the brain. 

 The small tumours are found attached by pedicles, but the 

 larger ones are usually floating in the cranial cavity, and 

 pressing injuriously against the brain. 



Some extraordinary cases have been recorded of growths 

 which have attained the size of an ordinary ox's brain, and 

 which have induced no apparent disorder until the animal's 

 sudden death. One of these products the largest on record 

 is in the Milan Museum, and was first described as an ossi- 

 fied brain. It has been the subject of many discussions, and 

 it has been satisfactorily proved to be one of the ordinary 

 bony growths from the inner plate of the cranial bones. 

 The late Professor Alessandrini of Bologna carefully exa- 

 mined many specimens in the fresh condition, and all have 

 been evidently connected at one period or other by a 

 decided bony attachment with the skull-cap. 



In the horse, the bony tumours consist in growths of a 

 detinal-like substance, invading usually the temporal bones. 

 They are probably aberrations in the development of dental 

 pulps, just like the tooth products connected so frequently 

 with fistula on the external surface of the temporal bones. 

 These growths in the horse, like the bony cranial tumours 

 of cattle, only induce symptoms when, either from their 

 size or mobility, they press injuriously on the brain. They 

 thus induce paralysis, blindness, and usually fatal disturb- 

 ance of vital organs, such as cheeked respiration, &c. 



DEPOSITS IN THE MEMBRANES OF THE BRAIN. 



In connection with the membraneous coverings of the 



