Explore chapters and articles related to this topic
Introduction: Background Material
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Beyond the diencephalon is the cerebrum (Figure 1.7), comprising the cerebral cortex and the basal ganglia. The cerebral cortex, basal ganglia, and the amygdala – a structure in the medial temporal lobe, just anterior to the hippocampus – constitute the telencephalon. The diencephalon and telencephalon are referred to as the forebrain. The basal ganglia and thalamus are more clearly illustrated in the frontal section of Figure 12.6. The cerebral cortex, where the word cortex refers to a rind or outer covering, is divided into the neocortex, which in humans is almost the whole of the cerebral cortex, and the phylogenetically older allocortex. The cerebral cortex constitutes in humans about 77% of the brain by volume and up to 40% by mass. It is the highly convoluted, outer layer covering the two cerebral hemispheres. Its thickness varies between different regions from less than 2 mm to about 4.5 mm. It contains about 16 billion neurons in a well-defined structure of up to six layers in the neocortex, labeled I–VI, layer I being the most superficial. The large folds, or convolutions, of the cerebral cortex are called gyri (singular, gyrus) and are separated by fissures known as sulci (singular, sulcus). Some of the deep fissures are used as landmarks that divide the neocortex into four lobes that can be identified on the outer surface of each hemisphere: the frontal, temporal, parietal, and occipital lobes (Figure 1.9). The central sulcus separates the frontal lobe from the parietal lobe, and the lateral sulcus separates the temporal lobe from the parietal and frontal lobes. Two other lobes are tucked inside the cerebral hemispheres: (i) the limbic lobe, which is an arc-shaped region on the medial surface of each cerebral hemisphere, and is contiguous with parts of the frontal, parietal, and temporal lobes, and (ii) the insular lobe, located deep within the lateral sulcus. The cerebral cortex is involved in higher functions, including sensory perception, voluntary movement, conscious thought, and language.
A new small-sized penguin from the late Eocene of Seymour Island with additional material of Mesetaornis polaris
Published in GFF, 2021
Piotr Jadwiszczak, Marcelo Reguero, Thomas Mörs
– NRM-PZ A824 is a relatively well-preserved tarsometatarsus. Most of its dorsal side as well as trochleae with an adjacent area of the plantar surface are covered with the well-cemented matrix. The bone is 48.4 mm long (maximally), 18.1 mm wide proximally and 21.8 mm wide distally, whereas its midwidth amounts to 15.7 mm. After most of the matrix had been digitally removed from the specimen, it became possible to examine the most important aspects of its previously hidden outward appearance (Fig. 3G–L). The proximal vascular foramina are both quite large and elongate, especially in their dorsal openings, and only slightly more widely spaced plantarly. The proximal metatarsal III, that separates them, is deeply lowered in dorsal view. Taking into account the main axis of the bone, the medial foramen is clearly more adaxial than the medial hypotarsal crest. The medial intermetatarsal sulcus is shallow and short, its lateral counterpart is deep, quite wide, and can be traced up to the intertrochlear incisure. Both plantar sulci are very shallow, albeit long and rather noticeable. Distally, close to said incisure, the lateral sulcus (on both sides) is replaced by a longitudinal series of perforations. There is no clear trace of the distal foramen or at least its distal bony framing. The tuberosity for the insertion of the m. tibialis cranialis is spindle-shaped and moderately wide. The hypotarsus is quite well developed, and three crests are distinguishable. The medial crest is partly broken, the main hypotarsal sulcus is relatively wide. The sulcus for a tendon of the m. flexor hallucis longus is shallow, because of the low lateral framing. The intermediate hypotarsal crest is prominent, slightly overhanging the main sulcus, its plantar edge rounded. The surface for the origin of the m. abductor digiti IV is very poorly marked and separated from the lateral margin. The second metatarsal is very gently curved, although its medial margin seems to be straight along the middle section. The fourth metatarsal is straight. The third trochlea is (expectedly) clearly more robust than the other two.