336 NERVOUS SYSTEM. 



Of the Ligamenta Denticula. 



These bodies are narrow semi-transparent bands, and very 

 thin, which are placed one on either side of the medulla spina- 

 lis, between the pia rnater and the tunica arachnoidea. They 

 commence at the occipital foramen, and descending between 

 the anterior and the posterior fasciculi of the roots of the 

 nerves, terminate somewhat above the inferior extremity of the 

 medulla ^pinalis. 



Each one is, at its commencement, in front of the accessory 

 nerve, and in descending is rather nearer to the posterior than 

 to the anterior fasciculi. By its internal margin it adheres 

 with uniformity to the pia mater, but the external margin has 

 a very different arrangement; for it sends off at intervals from 

 twelve to twenty-four serrated or denticulated processes, which 

 for the most part are placed between the fasciculi of cervical 

 and of dorsal nerves. The extremities of these teeth are small, 

 rounded, and strong, are surrounded by the arachnoidea, and 

 adhere very firmly to the dura mater, being pointed down- 

 wards. The position and connexions of each ligamentum den- 

 ticulatum are such, as to make it serve as a fastening; which 

 use is additionally indicated by its fibrous texture, and by the 

 necessity that the medulla has for such fastening, in considera- 

 tion of its being so deficient in filling up the vertebral canal.* 



It is taught by many anatomists, that the ligamenta denticu- 

 lata, from the opposite sides, join at the lower end of the spi- 

 nal marrow to form the single cylindrical chord, just men- 

 tioned, that passes thence to the lower end of the spinal cavity, 

 and has been described as an emanation from the pia mater. 

 I am, however, induced to think with Meckel and others, that 

 general analogy is in favour of the latter. 



* An opinion has been advanced by Professor Pancoast that the pia mater of 

 the elephant, of the bullock, and of man, forms by its duplicature the ligamentum 

 denticulatum. The specimen of the former which I have seen in his possession 

 affords strong indications of that arrangement : at the same time, in examining 

 its point of origin in man from the dura mater at the foramen magnum, its dis- 

 tinctly fasciculated and tendinous character there, is in opposition to this con- 

 clusion : the fissures which separate it along its internal margin from the pia 

 jnater are also not favourable to this idea, which in other respects is plausible 

 and ingenious. Wistar's Anat. Vol. 2, p. 513. Phila. 1839, 



