Agriculture Reference
In-Depth Information
base of the teat the so-called papillary venous circle of
Fürstenberg. The venous blood is drained in both cranial
and caudal directions; the former passes through three
subcutaneous veins: one middle cranial mammary vein
(the main vein), and two lateral, right and left, cranial
mammary veins in continuation to the corresponding
external pudendal veins. The latter take the route of the
external pudendal veins through the ventral labial veins.
When the goat is not in lactation, the blood fl ows in a
caudal direction, because the valvules of the cranial
mammary veins do not allow the blood to fl ow through
them. In lactation, the blood fl ows through the cranial
mammary veins, whose valvules become ineffi cient
because the veins become considerably larger. The median
mammary vein can be palpated under the skin, especially
during the lactation period. The lymph drainage is pro-
vided by the superfi cial inguinal lymph nodes, known also
as mammary lymph nodes. They are located in a caudo-
dorsal position to each mammary gland, and are accessible
under the skin.
T HE B RAIN
The brain consists of the cerebrum and the cerebellum.
Both are located and protected within the brain cavity (see
Figure 6.22 ).
The cerebrum shows on the dorso-lateral aspects two
symmetrical hemispheres separated by the longitudinal
fi ssure. The hemispheres are provided with gyri (sing.
gyrus), prominent elevations separated by sulci (sing.
sulcus
=
groove)
and
fi ssures, and are parts of the
telencephalon.
The cerebellum consists of a median prominent part
called the vermis, and two symmetrical structures on both
sides of the vermis, called cerebellar hemispheres. The
vermis has gyri and sulci transversely oriented, whereas
the hemispheres are provided with small gyri and sulci
oriented in all directions. The cerebellum is part of the
metencephalon.
The brain is surrounded by meninges, two soft and one
tough connective tissue layers, which protect the brain
from the environment (especially shocks). All irregulari-
ties of the brain are intimately covered by the soft and
delicate pia mater. The latter is followed by the arachnoid,
looking like a spider web, which allows spaces for the
cerebro- spinal fl uid. The most external layer is the tough
one, the dura mater, fused with, or even replacing the
periosteum of the brain cavity. A fold of the dura mater
called falx cerebri penetrates within the longitudinal fi ssure
of the cerebrum. The cerebrum is separated from the cer-
ebellum by another fold of dura mater called tentorium
cerebelli membranaceum (see Figure 6.22). The hypophy-
sis (pituitary gland), which is hanging on the ventral aspect
of the brain is surrounded and protected by dura mater
under the name of diaphragma sellae, anchored on the sella
turcica of the fl oor of the brain cavity.
The brain is composed of fi ve major parts, in the fol-
lowing rostro-caudal order: the telencephalon , the dien-
cephalon , the mesencephalon , the metencephalon , and the
myelencephalon . The telencephalon consists of two hemi-
spheres, with the grey substance outside and the white
substance inside. Several nuclei (grey matter) are embed-
ded within the white matter. Also the olfactory brain is part
of the telencephalon. The diencephalon or intermediate
brain consists of fi ve major components. The hypophysis
(pituitary gland) and the epiphysis (the pineal gland) are
two parts. The mesencephalon is the midbrain, situated
between the diencephalon and the pons. The metencepha-
lon consists of a ventral structure, the pons and a dorsal
structure, the cerebellum. The myelencephalon is also
called medulla oblongata, or simply medulla, which con-
nects the brain to the spinal cord.
THE NERVOUS SYSTEM
Along with the endocrine system, the nervous system cor-
relates the adjustments and reactions of the organism to
internal and environmental conditions. It is anatomically
divided into the central and the peripheral nervous systems.
The central nervous system consists of the brain and the
spinal cord. The peripheral nervous system includes the
cranial and the spinal nerves and the autonomic nervous
system (the nuclei of the autonomic nervous system are
located within the central nervous system).
The functional component of the central nervous system
is the perikaryon, or nervous cell. It has a cell body and
two types of processes: dendrites and axons. The dendrites
bring the nervous infl ux to the neuron cell, and the infl ux
leaves the cell through the axon. The central nervous
system is organized into two categories of structures:
the grey matter and the white matter. Neuron cells and
nuclei (agglomeration of neuron cells) form the grey
matter, whereas the axons of the neuron cells represent the
white matter, organized in fascicles and tracts (of nerve
fi bers).
The Central Nervous System
As function, the central nervous system receives stimuli
from the environment, and the whole body processes them
and sends motor commands to the effectors (muscles,
glands, etc.) via the peripheral nervous system.
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