The foregoing account deals with some microscopic observations on the main anatomical features of the head of X. 1aevis, in both larval and young adult stages.

The arrangement of the lateral line sensory organs of the larva has been compared with that of the frog, and both are in general agreement with the distribution of similar organs in the Urodela.

The larval musculature is found to be similar to that of X. fraseri, described by Edgeworth. Notes regarding the changes occurring at metamorphosis are given.

The course of the head vein and internal carotid artery has been followed, as both blood-vessels are relevant to the study of the chondrocranium and nerves.

A complete study of the chondrocranium in different stages of larvae from the time of hatching up to metamorphosis reveals several points at variance with Kotthaus's findings. Metamorphosis results in marked changes in the auditory and nasal regions. The former region has been studied by de Villiers in the adult Xenopus, and is herein only briefly reviewed. In regard to the nasal region, an account is given of the cavities and cartilages, both conforming in essentials to the typical Anuran arrangement.

The hyobranchial skeleton of the larva and young frog are in close agreement with that of mature specimens investigated by Ridewood.

The cranial nerves have been studied in some detail, and are observed to depart in some respects from those of typical Anura. The composition of the various nerves is in agreement with that of both Anura and Urodela, but the arrangement of the nerves approaches that of such Urodela as Siren (Norris), Proteus (Benedetti), and Salamandra (Francis). This is perhaps most noticeable in the innervation of the upper jaw, for a maxillary nerve is not separated from the maxillomandibular stem as in most Anura; the general cutaneous supply to the maxillary region is derived in Xenopus from the ramus ophthalmicus profundus V as in some Urodela.

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