The midbrain is represented chiefly by the optic lobes, the cortex of which alone is homologous with the corpora quadragemina of the mammals.
It occurs in two different forms. In the Ratitae, except Rhea, it consists mainly of a right and left united half (corpora fibrosa), with a deep longitudinal furrow on the dorsal side, and much resembles the same organ in crocodiles and tortoises.
The structure of the corpora cavernosa consists of a strong fibrous coat, the tunica albuginea, from the deep surface of which numerous fibrous trabeculae penetrate the interior and divide it into a number of spaces which are lined with endothelium and communicate with the veins.
Between the two corpora cavernosa the sheath is not complete and, having a comb-like appearance, is known as the septum pectinatum.
His discoveries, co-ordinated and arranged in vast corpora inscriptionum, stand now alongside Herodotus or Livy, furnishing a basis for their criticism.
