4 The Structure of the Spinal Cord of tlie Ostrich 



bution from the pia and dura, which, through the intervertebral foramina, 

 is directly continuous with the peripheral nerve-sheaths; this tissue 

 furnishes the capsule and framework for the spinal ganglia, which are 

 found just external to the foramina and attached to the fibres of the 

 dorsal roots. 



The pia, in contrast to the two more external membranes, forms, as 

 we may say, an integral part of the structure of the cord, and serves to 

 some extent as a framework, inasmuch as it is closely adherent to the 

 peripheral layer of neuroglia and follows the outline of the cord entering 

 all clefts and depressions. In the anterior median fissure it sinks to the 

 bottom as a thick, strong lamella, septum ventrale, supporting, just ven- 

 tral to the anterior commissure, the arteria meduUaris ventralis. 



The pia throughout is richly supplied with blood-vessels. Brandies 

 from these supply the cord, penetrating from the periphery inward and 

 from the arteria med. ventr. outward. The vessels carry with them a 

 connective tissue adventitia derived from the pia. In no case, however, 

 were processes of pia seen entering the substance of the cord except as 

 accompanying blood-vessels. This is easily demonstrated in specimens 

 over-stained with iron hgematoxylin and differentiated with picro- 

 fuchsin. In such preparations the vessels, together with their connective 

 tissue support, are stained brilliant red in contrast to the yellow-brown 

 neuroglia septa which might otherwise be mistaken for pia. 



-At three places in its circumference, the pia receives an accession of 

 thick dura like connective tissue fibres, producing ligamentous forma- 

 tions which extend as three longitudinal bands, lens-shaped in cross- 

 section. Two of these are situated laterally, Ugamenta longitudinalia 

 lateralia, and one is situated at the attachment of the septum ventrale. 

 Ugamentum longitudinale ventrale. The former corresponds to what 

 Berger^ has described as the Ugamentum dentatum in reptiles. Be- 

 tween the 37th and 38th segments in the region of the lumbo-sacral en- 

 largement, these bands reach a special development; they become much 

 stronger and are modified in form. From the ligamentum long, ventr. 

 pointed, tooth-like processes extend laterally to join the ligamenta long, 

 lat. These processes fit closely in the intersegmental grooves, the sulci 

 transversi, of the ventral surface of the cord. This is represented in 

 Fig. 3, a. 



A resemblance between this structure and the diiral tissue is at once 

 noticed, but it is identified as modified pia from the fact that the arach- 



" Berger, Ueber ein eigenthumliches Riickenmarksband einigen Reptilien 

 und Amphibien, Sitzb. Wiener Akad. Wiss., Bd. Ixxvii, 3 Abth. 



