SUMMARY.  A general account of the palate, nasal and vomeronasal organs throughout the Squamata is given, since these structures are intimately related to the lachrymal duct.  The bony palate of lizards shows variations in the extent to which the adjacent borders of the maxillary palatal processes and vomers are approximated behind the level of the opening of the duct of Jacobson's organ (fenestra vomeronasalis externa). separating this opening from that of the choana (fenestra exochoanalis).  In snakes the bony palate is highly modified, the maxillae are reduced and in many forms the fenestra vomeronasalis externa is bordered laterally by the septomaxilla.  In most lizards the superficial palate (soft tissues between the bony palate and the month) is incomplete, the vomerine and maxillary portions being divided by a groove, the choanal groove. This usually terminates anteriorly in relation to the duct of Jacobson's organ and posteriorly opens into the choana. In some lizards the choanal groove. are reduced, and in snakes they are entirely absent, so that the superficial palate is complete.  The relations of the lachrymal duct to the organ of Jacobson and choanal groove in a relatively large number of squamate types are deseeibed. In all forms the lachrymal duct opens anteriorly in close proximity to the duct of the organ of Jacobson. Behind this level the lachrymal duct may or may not communicate with the choanal groove.  The ontogeny of the structures considered is described in general terms, and it is shown that both the duct of Jacobson's organ and the choanal groove represent persistent portions of the primitive choana. The variations in relationships and extent of the choanal grooves are explained mainly on the basis of variations in the degree of fusion between the maxillary and vomerinc processes during ontogeny.  The condition in Squamata is compared with that in Sphenodon, where the lachrymal duct opens only into the lateral aspect of the nasal sac. It is shown that the essential difference between Sphenodon and the Squamata lies in the forward extension of the lachrymal duct to come into relationship with the duct of Jacobson's organ in lizards and snakes. This involves an invasion by the growing lachrymal duct of the tissues derived from the vomerine process. It is concluded that conditions in Sphenodon are primitive and could readily undergo elaboration along either the squamate or mammalian lines of evolution.  Certain functional implications of the conditions described are discussed. In the Squamata the organ of Jacobson is more highly developed than in any other vertebrates, and in many lizards the ciliated choanal grooves play an mportant part in conveying odorous particles to its lumen. In forms where these grooves are small or absent it is usually possible for the particles to be inserted directly by the tongue tips; there is is evidence, however, that there may also be some other filling mechanism, the nature of which remains obscure.  The constant relationship between the opening of the lac...

Summary 1. Current theories of ophidian evolution suggest that the snakes have been derived either from aquatic, above‐ground terrestrial, or burrowing ancestors. It is generally supposed that the ancestors of snakes, irrespective of their habits, were closely related to the platynotid lizards. In the absence of adequate palaeontological data, the respective merits of these assumptions must mainly be assessed on evidence obtained from study of living forms. 2. The close relationship between the snakes and lizards is pointed out in this article, and the main characteristics of the different families of fossil and living snakes are reviewed. 3. Many important features of the snakes as a group are described and their functional significance is discussed. Comparison with the corresponding condition in lizards is made. Ophidian characters regarded as being of particular significance include the bony investment of the forebrain, the platytrabic chondrocranium with absence of the interorbital septum and endocranial side‐walls, the absence of the epipterygoids and temporal arcades and the extreme mobility of the jaw skeleton in most forms; the presence of zygosphenal articulations throughout the vertebral column; the elaboration of the trunk musculature and ventral scales; the extreme concentration of alkali‐metal cation on the secretory side. (For reviews of evidence, see Crane (1950), Hokin & Rehm (1947), Rehm (1950).) (2) When the two sides of the mucosa are connected electrically, a current of relatively large magnitude can be maintained which requires the continuous performance of electrical work (Rehm, 1943; Rehm & Hokin, 1948; Crane, Davies & Longmuir, 1946, 1948 a; Crane & Davies, 19486). (3) There is a fall in the p.d. across the mucosa with the onset of secretion, but once secretion is well established further increases in the rate of secretion can occur with only small changes in the p.d. (cf. Crane, 1950; Rehm, 1944; Rehm, 1950). (4) The change from the non‐secretory to the secretory state and back is always associated with concomitant changes in the electrical parameters of the mucosa, whether these changes occur spontaneously or by drug action. In the absence of oxygen and in dead mucosae both p.d. and acid secretion are abolished (cf. Crane, 1950; Rehm & Hokin, 1947; Rehm, 1950). (5) Passage of electric current (c. 1 mA./cm.2) through the mucosa from an external source increases or decreases the rate of secretion of acid by a secreting mucosa according as the applied current enhances or opposes the spontaneous potential measured between calomel electrodes on either side of the mucosa (Rehm, 1945; Crane et al. 1946, 19486). (6) Passage of current does not initiate secretion in the dog (Rehm, 1945) but may do so in the frog (Crane et al. 1948 b). These results were obtained with intact gastric mucosa, and because of the technical difficulties involved it has not, so far, been possible to obtain direct information regarding the detailed electric changes in and around the oxyntic cells. A difficulty is that th...

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Summary.  Some features of the cranial anatomy, including the chondrocranium, of the burrowing lizard Anniella pulchra are described, mainly from serial sections.  The skull shows marked elongation of the temporal region, reduction of the orbits, loss of the temporal arcades and obliteration of the parieto‐occipital angle, so that the skull contours are streamlined.  The cranial kinesis is thought to be mainly of the mesokinetic type.  Basitrabecular processes, menisci and small epipterygoids are present. The parietal bones possess extensive downgrowths which partly enclose the cranial cavity on either side.  The chondrocranium shows great reduction in the orbito‐temporal region. A low interorbital septum, narrow planum supraseptale and taeniae marginales are present. There are no pila metoptica or pila accessoria and the taeniae mediales are represented only by embryonic rudiments. There are no discrete optic foramina, the optic nerves passing back to the chiasma above the trabecula communis.  The eyes are small but can hardly be regarded as degenerate; eyelids, nictitating membrane, lachrymal canaliculi and retractor bulbi muscles are present.  The tympanic membrane, tympanic cavity and Eustachian tubes are absent. The columella is massive with a small extra‐columella.  Conditions in Anniella are compared with those in other burrowing lizards, especially with Anguis fragilis, the skinks Nessia sp., and Acontias meleagris, and amphisbaenids. The main structural features associated with burrowing adaptation in lizards are described.  In spite of marked burrowing specialization, the cranial anatomy of Anniella resembles that of more typical Sauria in many important respects, and lacks aberrant features such as are present in amphisbaenids.